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Joshua Lederberg

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Joshua Lederberg (born May 23, 1925, Montclair , N.J., U.S.—died Feb. 2, 2008, New York , N.Y.) was an American geneticist and a pioneer in the field of bacterial genetics . He shared the 1958 Nobel Prize for Physiology or Medicine (with George W. Beadle and Edward L. Tatum ) for discovering the mechanisms of genetic recombination in bacteria .

Lederberg studied under Tatum at Yale (Ph.D., 1948) and taught at the University of Wisconsin (1947–59), where he established a department of medical genetics . In 1959 he joined the faculty of the Stanford Medical School, serving as director of the Kennedy Laboratories of Molecular Medicine there from 1962 to 1978, when he moved to New York City to become president of Rockefeller University . He held that post until 1990.

With Tatum he published “Gene Recombination in Escherichia coli ” (1946), in which he reported that the mixing of two different strains of a bacterium resulted in genetic recombination between them and thus to a new, crossbred strain of the bacterium. Scientists had previously thought that bacteria only reproduced asexually—i.e., by cells splitting in two; Lederberg and Tatum showed that they could also reproduce sexually, and that bacterial genetic systems are similar to those of multicellular organisms.

While biologists who had not previously believed that “sex” existed in bacteria such as E. coli were still confirming Lederberg’s discovery, he and his student Norton D. Zinder reported another and equally surprising finding. In the paper “Genetic Exchange in Salmonella ” (1952), they revealed that certain bacteriophages (bacteria-infecting viruses) were capable of carrying a bacterial gene from one bacterium to another, a phenomenon they termed transduction .

Lederberg’s discoveries greatly increased the utility of bacteria as a tool in genetics research, and it soon became as important as the fruit fly Drosophila and the bread mold Neurospora . Moreover, his discovery of transduction provided the first hint that genes could be inserted into cells. The realization that the genetic material of living things could be directly manipulated eventually bore fruit in the field of genetic engineering , or recombinant DNA technology .

At the dawn of space exploration , Lederberg coined the term exobiology to describe the scientific study of life outside Earth’s atmosphere. He later served as a consultant to NASA ’s Viking mission to Mars .

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Esther Lederberg changed our understanding of how bacteria breed

By Lina Zeldovich

Posted on May 23, 2022 11:00 AM EDT

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The annals of science journalism weren’t always as inclusive as they could have been. So  PopSci  is working to correct the record with  In Hindsight , a series profiling some of the figures whose contributions we missed. Read their stories and explore the rest of our 150th anniversary coverage  here . 

On December 10, 1958 , microbiologist Esther Lederberg stood next to her husband. Clad in a pale, floor-length gown, clutching a small purse in gloved hands, she gazed unsmiling into the camera. Joshua Lederberg had just won a Nobel Prize in Physiology or Medicine for his discoveries in bacterial genetics. 

For him, it was the spectacular peak of his career. For her, a bittersweet moment. Esther had worked with Joshua in a lab for more than a decade. She had helped him earn the highest recognition in science, yet he shared the award with two male researchers. Meanwhile, she was marked not as a brilliant scientist, but a brilliant scientist’s wife. 

Born in New York City in 1922, Esther Miriam Zimmer grew up during the Great Depression. Her family owned a printing business, but money was tight—meat was a rare treat, and lunch often consisted of a slice of bread topped with tomato juice. As a child, she impressed her family with her language abilities; she mastered Hebrew, and graduated high school at 15 with awards for French and Spanish. The obvious and acceptable path for this bright young woman would have been to earn a teaching degree at Hunter College. She pursued biology instead. Biographer Thomas E. Schindler—whose account was the first in-depth look at Lederberg and a key source of insights into her life—speculated that she might have fallen in love with it after reading Microbe Hunters , a science bestseller from 1926 . After a master’s in genetics at Stanford University, she moved back to New York in 1945.

A year later, at a post-war symposium at Cold Spring Harbor, which focused on heredity and variation in microorganisms, she met Joshua Lederberg. The pair married on December 13, 1946. To celebrate, the newlyweds attended a lecture on the mutagenic effects of nitrogen mustards—toxic chemicals designed for warfare, some of which were also tested as cancer treatments. Eventually, they settled down together at the University of Wisconsin (now the University of Wisconsin-Madison) where they both focused on bacterial genetics.

The two researchers complemented each other. Joshua was a big picture thinker, but not a bench worker, while Esther was a keen experimenter with dexterous laboratory hands. Joshua came up with novel terms like plasmids and microbiomes, and Esther made his ideas bloom in petri dishes. Joshua proved that bacteria could exchange genes with one another, but it was Esther who prepared the cultures for many of his experiments. 

Many of those experimental protocols were extremely tedious and time-consuming. For some of them, she had to lift tiny samples of bacterial colonies with a sterile needle and transfer them to new plates—sterilizing the needle, and repeating it again, and again. One day in 1951, she had an idea that originated from her make-up kit: Like many other women, she powdered her face using a pad of velveteen cloth. She wondered what would happen if she pressed the soft fabric onto a bacteria-seeded petri dish and then pressed it onto a clean plate. Would it leave a microbial imprint similar to the ink stamps from her family’s printing business? When she tried it, the germs in the second dish turned out to be an exact copy of the original. That tinkering evolved into a new technique named replica plating, which remains a laboratory staple to this day. 

That wasn’t Esther’s only lasting contribution. She also discovered, for the first time, a bacteria-targeting virus that hid inside its host genome instead of killing it. She named it “phage lambda,” and the finding helped scientists understand how viruses transfer DNA from one bacterium to another (transduction) as well as how bacteria swap their own DNA (horizontal gene transfer)—concepts now harnessed to develop genetic therapeutics and other drugs. When she followed Joshua to Stanford after he won the Nobel, she was the inaugural director of the Plasmid Reference Center at Stanford University until 1986, a year after her official retirement.

The prize, however, tipped the delicate balance of Esther and Joshua’s life in his favor. He came to lead the newly created department of genetics at Stanford while Esther’s position didn’t even offer tenure. This phenomenon is called the Matilda Effect (named for American suffragist Matilda Gage, who described it in her essays in the 1800s) in which women’s scientific contributions are credited to men or overlooked. Conversely, many well-known male researchers enjoy the Matthew Effect, in which other people’s work is more likely to get attributed to them.

The Lederbergs’ marriage fell apart in the wake of the Nobel, and they divorced eight years later. In 1993, Esther married Matthew Simon, a mathematical linguist. After she died in 2006, he spent years plowing through her records and photos in order to put together a memorial website in her honor—and help give her a legacy all her own. 

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Rockefeller University

1958 nobel prize in physiology or medicine.

By the mid-20th century, science had established several crucial facts about the capabilities of bacteria, a seemingly primitive, unicellular organism first classified in 1676. Some bacteria, scientists understood, can cause life-threatening disease; some are resistant to even the strongest antibiotics; and some that are neither virulent nor resistant to begin with can gain both virulence and resistance. The question of how bacteria accomplish such sleight of hand, which had been subject to decades of logical but inaccurate speculation, was resolved by a 22-year-old graduate student in 1947. Joshua Lederberg, Rockefeller University’s fifth president, won a share of the 1958 Nobel Prize in Physiology or Medicine for his discoveries of genetic transfer in bacteria.

Through the 1940s, scientific wisdom had it that bacteria do not have genetic mechanisms similar to those of higher organisms. The prevailing hypothesis, taught in Dr. Lederberg’s Columbia University medical school classes, classed bacteria with schizomycetes, organisms that reproduce by cloning. The 1944 discovery of Rockefeller scientists Oswald T. Avery, Maclyn McCarty and Colin MacLeod that deoxyribonucleic acid, or DNA, is the genetic material in Pneumococcus proved that bacteria have genes and thus drew an unexpected parallel between bacteria and higher organisms. But their discovery, unconnected to a method of proliferation, was met with widespread skepticism. Inspired by the new evidence, Dr. Lederberg interrupted medical school to pursue experimental genetics with Edward L. Tatum, the Yale University chemist with whom he would later share the Nobel Prize.

Initial experiments with the intestinal bacteria Escherichia coli led Dr. Lederberg to estimate that only one in 20 strains are fertile, and that if bacteria mate, they do so only during a particular phase of their life cycle. After crossing two strains of E. coli, each with different mutations for nutritional deficiencies, he found that some of the offspring of each strain had regained the ability to produce the nutrients its parent could not. When that ability continued to be inherited by successive generations, Dr. Lederberg had effectively proved the textbooks wrong. He named the bacterial mating process conjugation, received his Ph.D. for this research and officially left medical school to continue in bacterial genetics. We now understand that bacterial mating occurs only through cell-to-cell contact, when a bridge is formed between the two cells that transports genetic information from the donor cell to the recipient.

Dr. Lederberg’s experiments also identified E. coli as a haploid that carries only a single chromosome and suggested that conjugation is a form of unequal horizontal gene transfer: Rather than exchanging genes equally, the mating bacteria transfer partial genetic material from one parent to the other. He also developed a technique that allowed for the identification of antibiotic- or bacteriophage-resistant strains without exposing the bacteria to the phage or the drug, and proved that resistance is a genetic mutation rather than an adaptation.

Following his seminal research at Yale, Dr. Lederberg accepted a position to chair the newly founded department of genetics at the University of Wisconsin, Madison. With his graduate student Norton Zinder — later a colleague at Rockefeller University — Dr. Lederberg showed that bacteriophages can transfer genetic information between cells in Salmonella. The process, which they named transduction, was the first demonstration that it is possible to introduce new genes into an organism and in other ways manipulate its genetic material. The discovery explained how different species of bacteria can so quickly gain resistance to the same antibiotic.

The scientific contributions of Dr. Lederberg’s pathbreaking foray into bacterial genetics are legion. His work gave scientists an experimental model whose simplicity and rapid growth made it ideal for genetic studies. His description of bacterial conjugation led directly to the distinction denoted since 1962 by the terms prokaryotic and eukaryotic. His findings led to research that elucidated the mechanisms of bacteriophages and other viruses; explained how cell growth is interrupted; and clarified how cancer progresses. And his description of transduction led to the development of gene therapy and contributed to the boom in biotechnology and genetic engineering in the 1970s. Dr. Lederberg received half of the 1958 Nobel Prize “for his discoveries concerning genetic recombination and the organization of the genetic material of bacteria. Dr. Tatum and his colleague George Wells Beadle received the second half of the 1958 prize “for their discovery that genes act by regulating definite chemical events.”

Born in 1925 and raised in New York City, Dr. Lederberg received his Ph.D. from Yale University in 1947 and then joined the University of Wisconsin, Madison, where he founded the department of medical genetics 10 years later. In 1959, he moved to Stanford University, where he was chair of the newly established department of genetics. There he also expanded his research into the fields of artificial intelligence and exobiology. In 1978, Dr. Lederberg became the fifth president of The Rockefeller University, a position he held until 1990, when he retired from the presidency and became University Professor and head of the Laboratory of Molecular Genetics and Informatics, where his research continued. Throughout his later research career, Dr. Lederberg was highly active in international science and human rights advocacy, serving as a public policy adviser to nine United States presidential administrations and authoring a weekly Washington Post column, “Science and Man,” for six years. He was a member of the National Academy of Sciences and a foreign member of The Royal Society. In addition to the Nobel Prize, he received the National Medal of Science and the Presidential Medal of Freedom. He died in New York in 2008.

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• Joshua Lederberg - Biographical

Joshua Lederberg

Biographical.

J oshua Lederberg was born in Montclair, N.J. on May 23, 1925. He was brought up in the Washington Heights District of Upper Manhattan, New York City, where he received his education in Public School 46, Junior High School 164 and Stuyvesant High School. From 1941 to 1944 he studied at Columbia College, where he obtained his B.A. with honours in Zoology (premedical course), and from 1944 to 1946 at the College of Physicians and Surgeons of Columbia University Medical School. Here he carried out part-time research with Professor F.J. Ryan in the Department of Zoology. Subsequently he went to the Department of Microbiology and Botany at Yale University, New Haven, Conn., as Research Fellow of the Jane Coffin Childs Fund for Medical Research and, during 1946-1947, as a graduate student with Professor E.L. Tatum . He was awarded his Ph.D. degree in 1948.

In 1947, he was appointed Assistant Professor of Genetics at the University of Wisconsin, where he was promoted to Associate Professor in 1950 and Professor in 1954. He organized the Department of Medical Genetics in 1957, of which he was Chairman during 1957-1958.

Stanford University Medical School entrusted to him the organization of its Department of Genetics and appointed him Professor and Executive Head in 1959. Since 1962, he has been Director of the Kennedy Laboratories for Molecular Medicine.

Lederberg was Visiting Professor of Bacteriology at the University of California, Berkeley, in 1950; and Fulbright Visiting Professor of Bacteriology at Melbourne University, Australia, in 1957. In the latter year, he was also elected to the National Academy of Sciences (USA).

While at Yale, Lederberg married Esther M. Zimmer in 1946. They have no children. Mrs. Lederberg had obtained her M.A. at Stanford with Professor G.W. Beadle during 1944-1946, and her Ph.D. degree at the University of Wisconsin in 1950. She is working full time as research associate.

This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel . It was later edited and republished in Nobel Lectures . To cite this document, always state the source as shown above.

Addendum, December 1997

Joshua Lederberg was born in Montclair NJ, near New York, the son of Rabbi Zwi H. and Esther Lederberg, recently emigrated from Israel, on May 23 1925. He was educated in New York. After a period of study at Columbia P&S medical school, where he began his life-long research in molecular biology, he received his Ph.D. in microbiology at Yale. Then he served as professor of genetics at the University of Wisconsin, then at Stanford School of Medicine, before coming to the Rockefeller in 1978. His life long research, for which he received the Nobel Prize in 1958 (at the age of 33), has been in genetic structure and function in microorganisms. He has been actively involved in artificial intelligence research (in computer science) and in the NASA experimental programs seeking life on Mars. He has also been a consultant on health-related matters for government and the international community, e.g. having had long service on WHO’s Advisory Health Research Council. He received the US National Medal of Science in 1989, where his consultative role was specifically cited. He has been a member of the National Academy of Sciences since 1957, and a charter member of its Institute of Medicine, has served as Chairman of the President’s Cancer Panel, and of the Congress’ Technology Assessment Advisory Council, as well as on numerous other consultative panels.

From 1978 to 1990, he served as president of the Rockefeller University. He continues his research activities there in the field of interactions of gene functionality and mutagenesis in bacteria. His current station there is Sackler Foundation scholar and professor-emeritus of molecular genetics and informatics.

His wife Marguerite Stein Lederberg was born in Paris, was educated as a physician in the U.S. and now serves as Clinical Professor of Psychiatry at Memorial Sloan Kettering Cancer Center in New York. They have two children, David Kirsch and Anne Lederberg.

Addendum, June 2005

Please consult http://profiles.NLM.nih.gov/BB for extensive archival and biographical detail. The focus of my research has shifted to “What is the fastest rate possible for the growth of a bacterial cell, (and why?)”.

J oshua Lederberg died on February 2, 2008.

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• Published: 26 March 2008

Joshua Lederberg (1925–2008)

• Baruch S. Blumberg 1  

Nature volume  452 ,  page 422 ( 2008 ) Cite this article

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Decisive discoveries in bacterial genetics.

I think it was 1941 when I first met Josh Lederberg. The location was the American Institute Science Laboratory in New York city, in the shadow of the Empire State Building. These labs were established to enable high-school students to conduct after-school research, and were an inspiring place for the science nerds of the time. Lederberg and I had much in common. We were born in the same year, spent much of our youthful spare time in branches of the New York Public Library, and were prompted to enter medical research by reading Paul de Kruif's Microbe Hunters .

Even then, his talent and energy marked him out. Lederberg, who died on 2 February 2008, became a brilliant biologist and an exceptional leader whose influence extended to space science and computing.

He was educated at Stuyvesant High School, an élite institution that produced four Nobel laureates in science, and then Columbia University. But before completing his medical education at Columbia he migrated to Yale University to do research. Inspired by Oswald Avery's discovery that DNA, not protein, is the genetic material in Pneumococcus , he embarked on testing the widely held hypothesis that bacteria simply divide into two offspring from a single genome. Lederberg, however, showed that sexual reproduction occurs in Escherichia coli , so revealing both an unexpected feature of microbial reproduction and providing an essential tool for genetic research and biotechnology.

More was to come following the award of his PhD in 1947 and a move in that same year to the University of Wisconsin, Madison. Together with colleagues, including Esther Zimmer (to whom he was then married) and Norton Zinder, he discovered that viruses that infect bacteria can transfer genetic information between their hosts. This mechanism — transduction — was an unexpected way of altering the host's genetic make-up, and later assumed special significance with the recognition that viral sequences can be inserted in the human genome and can presumably be inherited. The discovery of transduction opened a vast area for research on the role of viruses in evolution and disease, and — even more intriguing — into the non-pathological characteristics of microorganisms.

Another surprise was the finding that small, ring-shaped pieces of DNA, termed plasmids, reside in microbial cells and are distinct from chromosomal DNA, being capable of autonomous replication. Plasmids can be introduced into other cells to produce vast amounts of useful proteins such as human insulin and the hepatitis B virus vaccine. Lederberg's work was seminal in initiating a new approach to biology based on the genome and its interactions with the environment. This was recognized by the award of the Nobel prize in 1958, at the age of 33, which he shared with George Beadle and Edward Tatum.

By then he was already widening his horizons, stimulated in particular by the launch of Sputnik on 4 October 1957. He was excited by the prospect of space exploration, but was also concerned about possible biological cross-contamination between Earth and other planetary bodies. In December 1957 he wrote to the US National Academy of Sciences (NAS) to warn of this danger. The eventual consequence was that objects and crews returning from Moon missions were subject to decontamination and quarantine.

Lederberg was appointed as a founder member of the NAS Space Science Board in 1958, and continued to stimulate both professional and public interest in biological space research (particularly in his “Science and Man” columns in The Washington Post ). He coined the word 'exobiology', which signalled the arrival of the discipline dedicated to the search for extraterrestrial life. This term was criticized as inappropriate, because there was no life known beyond Earth, and as designating a discipline without a subject. Its descendant discipline is 'astrobiology', a term often used interchangeably with exobiology. Astrobiology involves study of the origins of life on Earth, and testing the hypothesis that life exists elsewhere, maintaining Lederberg's vision of biology as an essential component of space research.

His connection with space science became especially close when he was involved in planning, along with colleagues, experiments to be carried by the Viking landers to seek evidence of microbial life on Mars. The experiments consisted of the collection and spectrometric analysis of soil samples, and the landers commenced operations in 1976. The results were inconclusive, but they marked the beginning of a search that continues in the astrobiology programmes in the United States and elsewhere.

Stimulated by his space research, Lederberg became a pioneer in the use of computers for biology and medical science. The DENDRAL program aided the determination of chemical structures from the spectrometric data collected on the Viking mission. Later, it was used to characterize structures of other compounds and was eventually applied to the organization and analysis of large biomedical data sets. This in turn led to medical 'expert systems', including INTERNIST, an expert system for clinical diagnosis and treatment.

As if all of this were not enough, Lederberg took on senior management responsibilities at Stanford University, to which he moved in 1959, and other institutions, culminating in his appointment in 1978 as president of the Rockefeller University in New York. He served on various prominent committees and agencies, and was an adviser to many US presidential administrations. He was concerned about the hazards of biological warfare and was a consultant to the US Arms Control and Disarmament Agency, and served on the Defense Science Board, which advises the Department of Defense. He was also a member of the science advisory board of the NASA Astrobiology Institute, an intellectual offspring of his early interests in space biology. In 2006 he was awarded the US Presidential Medal of Freedom.

As a researcher, Lederberg emphasized the importance of honesty and clarity in reporting scientific results. He recognized that science is a powerful problem-solving tool but that it has its limitations for individuals and society. His father was a rabbi and may have wanted his son to follow in his footsteps, which perhaps prompted Josh's awareness that acquiring knowledge is a blessing, yet comes laden with obligations.

Scientists are not usually thought of as heroes. I write as an old friend and colleague, but to my mind Joshua Lederberg was just such a man. Through his far-ranging interests and achievements, often accomplished against entrenched opinions, he has left an enduring imprint on science.

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Concept 18 Bacteria and viruses have DNA too.

• Alfred Day Hershey (1908-1997)

Joshua Lederberg (1925-2008)

Joshua Lederberg was born in Montclair, New Jersey, and as he said in a 1998 interview , he must have been born a scientist. Lederberg showed an early aptitude and interest in science. In 1941, after high school, he entered Columbia University with the intention of studying medicine.

At Columbia, Lederberg became interested in Beadle and Tatum's Neurospora experiments, which opened up new and exciting research possibilities especially in the fledgling field of genetic analysis. In 1943, Lederberg got a job as a media-prep gopher in Frances Ryan's lab in the Department of Zoology. Ryan was a post-doc at Stanford in 1941-42, where he met Beadle and Tatum and became interested in using Neurospora as a research model. Ryan's mentorship and discussions with other faculty members and graduate students, "nourished [Lederberg's] education as a scientist." Lederberg found that scientific research was more intellectually challenging than the textbook drills of medical school.

From 1943-1944, Lederberg had a year of active duty in the United States Naval Reserves where he worked in a clinical parasitology laboratory at the U. S. Naval Hospital on Long Island, New York. He did not see active service, and although he was expected to return to medical school, at the end of 1944 Lederberg was back working in Ryan's lab.

1944 was the year Oswald Avery and his group published their paper on the transforming ability of DNA. Lederberg was profoundly influenced by the paper and its unlimited implications. He and Ryan immediately tried doing similar experiments using Neurospora . Unfortunately, they were unable to get the necessary mutants. Lederberg started to think about using a bacterial system even though there was still debate about whether bacteria had genes or not.

An opportunity came to test his ideas. Edward Tatum was moving from Stanford to Yale to start a new microbiology lab. Ryan encouraged Lederberg to apply to work in Tatum's lab and Lederberg was accepted in 1946. Tatum already had some E. coli mutants that were suitable for the kind of experiment Lederberg outlined. Within six weeks, Lederberg had the results he needed to prove bacterial conjugation occurred. For this work, Lederberg shared the 1958 Nobel Prize in Physiology or Medicine with Edward Tatum and George Beadle.

After obtaining a Ph.D. from Yale in 1948, Lederberg accepted a job at the University of Wisconsin . It was at Wisconsin that Lederberg developed the technique of bacterial replica plating in which bacterial colonies can be duplicated onto filters for further analysis. Lederberg also helped create and later served as the chair of the Department of Medical Genetics .

In 1958, Lederberg left Wisconsin for the Department of Genetics at Stanford University's School of Medicine . At Stanford, in addition to his own bacterial research, Lederberg had two other interests. One was artificial intelligence; Lederberg helped develop one of the first computer systems (DENDRAL) that could make decisions using a specific set of algorithms and a database. Lederberg's other interest was exobiology. He was an active consultant on the Space Science Board of the National Academy of Sciences , and was greatly interested in the Mariner and Viking missions as well as the search for extraterrestial life.

In 1978, he was appointed President of Rockefeller University - the site of Oswald Avery's Pneumococcus research. From 1990, Lederberg was Professor Emeritus of Rockefeller University. He served on a number of government advisory boards and wrote a weekly column Science and Man for the Washington Post where he informed the public on issues in science and research. Lederberg's last project was to compile an informational web site at the National Library of Medicine using archival material he had accumulated over the years.

Joshua Lederberg was Edward Tatum's graduate student. Lederberg's wife Esther was George Beadle's graduate student.

Conjugation occurs only if bacteria are in close contact. Can you design an experiment that shows this is true?

Funded by --> The Josiah Macy, Jr. Foundation © 2002 - 2011, DNA Learning Center , Cold Spring Harbor Laboratory . All rights reserved.

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Classic Spotlight: the Discovery of Bacterial Transduction

Transduction, an indispensable genetic tool in many microbial systems, is the transfer of genetic information from a donor to a recipient cell via a virus particle. Although bacteriophages were first described early in the 20th century ( 1 , 2 ), their ability to transduce bacterial genetic traits was not appreciated until almost 4 decades later. The discovery and initial mechanistic description of transduction were reported in 1952 by Norton Zinder and Joshua Lederberg in the Journal of Bacteriology ( 3 ). The Zinder and Lederberg paper represents a key conceptual advance in microbial genetics but is not a particularly easy read for modern-day biologists. The experiments are presented blow-by-blow in a detective yarn style that features quaint language and arcane terminology. But what elegant experiments they were!

Zinder, a graduate student in Lederberg's laboratory at the University of Wisconsin, was attempting to demonstrate genetic exchange in Salmonella species using the approach developed by the Lederberg group that had revealed conjugation in Escherichia coli . Accordingly, he created a series of doubly auxotrophic Salmonella strains from different parental lines and plated pairwise mixtures of them on minimal medium to look for prototrophic recombinants. The reason for using multiply mutated strains was to reduce the background of spontaneous revertants and thereby enhance detection of any rare recombinants. This approach had worked well with the E. coli conjugation system, but only one pairwise combination of Zinder's 20 Salmonella lines consistently produced prototrophs above background levels. The productive strains were designated LT-2a and LT-22a (where “a” indicates multiply auxotrophic). Analysis of unselected genetic markers in the strains indicated that the prototrophic recombinants arose from the LT-22 parent, never the LT-2 parent. Two fortuitous factors, which only came to light subsequently, proved critical to this positive result. First, strain LT-22 harbored a temperate phage, now known as P22, that could infect and lyse the P22-sensitive LT-2 strain. Second, the two auxotrophic mutations in the LT-22 parent just happened to be tightly linked, allowing them to be corrected by a single transducing fragment, an amazing stroke of luck ( 4 ).

Zinder and Lederberg investigated the mechanism of genetic exchange with the productive LT-2/LT-22 strain pair. Their best-known experiment, prominent in microbial genetics texts, employed a U-tube and filter apparatus like the one devised by Bernard Davis to show that bacterial conjugation required cell-cell contact between the parental strains ( 5 ). Each strain was put in one arm of the U-tube, separated from the other by a filter impermeable to bacterial cells. This experiment showed that, in contrast to conjugation, the transduction of prototrophic alleles from LT-2 to LT-22 did not require cell-cell contact. Further U-tube experiments showed that transductants could be produced by mixing LT-22 with a sterile filtrate of an LT-2 culture but only if the LT-2 cells had prior exposure to a sterile filtrate of an LT-22 culture. A filtrable agent (FA) was evidently responsible for transduction activity. It must have moved from the LT-22 culture through the filter to the LT-2 side of the U-tube, where it induced FA activity, which then moved back across the filter to produce prototrophic recombinants in the LT-22 cells.

In further tests, FA exhibited many chemical, physical, and genetic properties synonymous with those of bacteriophage particles. (i) FA and P22 exhibited a common adsorption specificity, in which most “smooth” Salmonella strains adsorbed FA and phage P22 whereas “rough” strains did not. (ii) The time course of FA production paralleled that of phage P22 production after infection of LT-2 cells. (iii) FA and phage particles copurified and shared a common filtration endpoint. (iv) FA and phage particles were resistant to chloroform, toluene, and ethanol, impervious to proteases, RNase, and DNase, and inactivated by formalin.

Zinder and Lederberg concluded that FA “conforms to the genotype of the cells from which it comes … [and] has many activities, producing many different transductions. … FA may be considered as genetic material which enters the fixed heredity of the transduced cell. … There is good reason to identify the particle with bacteriophage. Nevertheless, the phage particle would function as a passive carrier of the genetic material transduced from one bacterium to another. This material corresponds only to a fragment of the bacterial genotype.”

Clearly, Zinder and Lederberg had discovered a versatile way to transfer small bits of genetic material from one bacterium to another. Their discovery marks the birth of Salmonella genetics, and transduction soon became a useful genetic tool for E. coli as well ( 6 ). Today, transduction enables microbiologists to map and manipulate genes in a wide variety of bacteria and archaea. I encourage readers who are not familiar with Zinder and Lederberg's landmark study to give it a read to see how outstanding scientists thought about and carried out microbial genetics experiments before much was known about the nature of the gene. An excellent retrospective article by Zinder ( 4 ) provides a rich historical context for the transduction story.

The views expressed in this Editorial do not necessarily reflect the views of the journal or of ASM .

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UC MUSEUM OF PALEONTOLOGY

Understanding Evolution

Your one-stop source for information on evolution

DNA and Mutations

Mutations are random.

Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not “try” to supply what the organism “needs.” Factors in the environment may influence the rate of mutation but are not generally thought to influence the direction of mutation. For example, exposure to harmful chemicals may increase the mutation rate, but will not cause more mutations that make the organism resistant to those chemicals. In this respect, mutations are  random  — whether a particular mutation happens or not is unrelated to how useful that mutation would be.

For example, in the U.S. where people have access to shampoos with chemicals that kill lice, we have a lot of lice that are resistant to those chemicals. There are two possible explanations for this:

Scientists generally think that the first explanation is the right one and that  directed mutations , the second possible explanation relying on non-random mutation, is not correct.

Researchers have performed many experiments in this area. Though results can be interpreted in several ways, none unambiguously support directed mutation. Nevertheless, scientists are still doing research that provides evidence relevant to this issue.

In addition, experiments have made it clear that many mutations are in fact random, and did not occur because the organism was placed in a situation where the mutation would be useful. For example, if you expose bacteria to an antibiotic, you will likely observe an increased prevalence of antibiotic resistance. Esther and Joshua Lederberg determined that many of these mutations for antibiotic resistance existed in the population even before the population was exposed to the antibiotic — and that exposure to the antibiotic did not cause those new resistant mutants to appear.

The Lederberg experiment

In 1952, Esther and Joshua Lederberg performed an experiment that helped show that many mutations are random, not directed. In this experiment, they capitalized on the ease with which bacteria can be grown and maintained. Bacteria grow into isolated colonies on plates. These colonies can be reproduced from an original plate to new plates by “stamping” the original plate with a cloth and then stamping empty plates with the same cloth. Bacteria from each colony are picked up on the cloth and then deposited on the new plates by the cloth.

Esther and Joshua  hypothesized  that antibiotic resistant strains of bacteria surviving an application of antibiotics had the resistance before their exposure to the antibiotics, not as a result of the exposure. Their experimental set-up is summarized below:

So the penicillin-resistant bacteria were there in the population before they encountered penicillin. They did not evolve resistance in response to exposure to the antibiotic.

A case study of the effects of mutation: Sickle cell anemia

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Lederberg on his discovery of conjugation

Breaking News

Esther Lederberg, 83; helped unlock mysteries of bacteria and viruses

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Esther Lederberg, the pioneering microbial geneticist whose crucial discoveries were overshadowed by those of her Nobel Prize-winning husband, Joshua Lederberg, died Nov. 11 at Stanford Hospital of pneumonia and congestive heart failure. She was 83.

She discovered the lambda phage, a parasite of bacteria that became a key tool for the laboratory study of viruses and genetics, and was the co-developer with her husband of replica plating, a technique for rapid screening of bacteria for desired mutations.

“She developed lab procedures that all of us have used in research,” said cancer researcher Stanley Falkow of the Stanford University School of Medicine.

She was also a pioneer of women’s rights, becoming a full professor at a time when women were rare on the faculties of Stanford and other major universities. “She was a real legend,” said Dr. Lucy Tompkins of Stanford.

A phage is a virus that infects only bacteria. Before Esther Lederberg’s work, the only known phages were so-called lytic phages that invade the bacterium, multiply rapidly and kill the host.

As a graduate student at the University of Wisconsin in 1950, she accidentally discovered the lambda phage -- the first known “temperate” phage. Temperate phages invade bacteria, but they insinuate themselves into the host’s DNA where they can persist as long as the cell is alive. The genetic information is stored in rings of DNA called plasmids.

Only when the cell is stressed, such as by a lack of nutrients, does the phage replicate, killing the host bacterium.

She was growing the common bacterium Escherichia coli in petri dishes when she noticed that some colonies had a “nibbled” appearance, like something had been chewing on them. Puzzled, she retrieved material from the gaps and found that it could produce the same phenomenon in other bacteria. The retrieved material proved to be the lambda phage.

The lambda phage became a laboratory model for more complicated animal viruses that have a similar life cycle, including some tumor viruses and herpes virus.

She laid the groundwork for demonstrating how phages can transfer genes between bacteria, and her findings were crucial to advancing the understanding of how genes are regulated, how pieces of DNA break apart and recombine to make new genes, and how the process of making RNA from DNA is started and stopped.

Building on her work, Joshua Lederberg won the 1958 Nobel Prize for Physiology or Medicine for his discoveries on how bacteria swap genes.

The couple working together also developed the technique known as replica plating.

Before their work, screening bacteria for a desired mutation was a straightforward but tedious procedure that might involve testing as many as 10,000 individual bacteria colonies. Their procedure had the simplicity of a rubber stamp.

Colonies of bacteria are typically grown in a petri dish or “plate” holding a medium that contains everything needed for their growth. The Lederbergs discovered that they could place a piece of velvet on the original plate, then place it on other sterile plates to transfer bacteria from each colony.

If such a replica plate lacks a nutrient critical for the bacterium’s growth, only mutants able to make the nutrient themselves will flourish. Alternatively, if the replica plate contains an antibiotic, then only those colonies resistant to it will flourish. The original antibiotic-sensitive bacterium can then be isolated from the original plate.

The discovery not only provided a rapid way to identify mutants, but it also proved that the mutations, such as antibiotic resistance, were already present in the original colonies and were not, as many scientists believed, developed upon exposure to the antibiotic.

Although the team eventually settled on sterile velvet cloth for the transfer, the original experiments were performed using the makeup applicator from Esther’s compact.

In her later years, Esther Lederberg was a seemingly limitless repository of information about the bacteria and phage strains she worked with, according to biochemist Dale Kaiser of Stanford.

Countless researchers worldwide reaped the benefits of her methodical records and near-photographic memory of the details of her strains, he said. From 1976 to 1986, she directed the Plasmid Reference Center at Stanford -- a repository of genetic information about phage genes.

She retired in 1985.

Esther Miriam Zimmer was born to a poor family in the Bronx, N.Y., on Dec. 18, 1922. She enrolled at Hunter College of the City University of New York, intending to study French or literature. But to the horror of her instructors, who thought science was for men only, she got diverted to biochemistry and received her bachelor’s degree in 1942.

She then went to Stanford to study genetics. She became a teaching assistant but was still so pressed for money, she later told her husband, that she took the frogs that were dissected in the lab and ate their legs for dinner.

She received her master’s degree in 1946, the same year she married Joshua Lederberg. Although three years younger than Esther, he was already on the faculty at the University of Wisconsin.

After graduation, she joined him there, received her doctorate in 1950 and became her husband’s research associate.

Joshua Lederberg came to Stanford in 1959 as head of the department of genetics, and Esther joined the department of microbiology and immunology. According to her second husband, Matthew Simon, she and two other women went to the dean to demand that he appoint a woman to the faculty. Lederberg got the position, Simon said, because she was the only one of the three that would accept a nontenured slot.

Stanford research associate Jonathan Hardy recalled her wit and charm and her ability to hold an audience captive with her tales about the scientists with whom she had worked. “Esther was a cheery person and had an excellent sense of humor,” he said, “but I believe she would want to be remembered mostly as a scientist, which she was, through and through, until her very last days.”

Outside the lab, she had an intense interest in medieval, renaissance and baroque music and medieval dance. In 1962, she founded the Mid-Peninsula Recorder Orchestra, which still draws amateur musicians to play compositions from the 13th century to the present.

She told the San Francisco Chronicle that she had originally wanted to play the flute, but picked up the recorder on a whim and immediately fell in love. “You can begin anytime, even though it takes a lifetime to be good,” she said.

After her 1966 divorce from Joshua Lederberg, she started a group at Stanford, primarily for divorced women, where they could talk about books, music and other shared interests. It later became something of a singles club.

In 1989, engineer Matthew Simon moved to Stanford and went to one of the club’s meetings. “I asked if there was anyone who knew about early music -- where to find it, and so forth,” he said. She overheard him and the two discovered they shared many common interests. They married in 1993.

“I was very lucky that I met a woman interested in music, Dickens, Jane Austen and many other things,” he said. “She was very well-rounded.”

She is survived by Simon and her brother Benjamin Zimmer.

[email protected]

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A Hidden Legacy: The Life and Work of Esther Zimmer Lederberg

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This biography of Esther Zimmer Lederberg highlights the importance of her research work, which revealed the unique features of bacterial sex, essential for our understanding of molecular biology and evolution. A Hidden Legacy relates how, she and her husband Joshua Lederberg established the new field of bacterial genetics together, in the decade leading up to the discovery of the DNA double helix. Their impressive series of achievements include: the discovery of λ bacteriophage and of the first plasmid, known as the F-factor; the demonstration that viruses carry bacterial genes between bacteria; and the elucidation of fundamental properties of bacterial sex. This successful collaboration earned Joshua the 1958 Nobel Prize, which he shared with two of Esther’s mentors, George Beadle and Edward Tatum. Esther Lederberg’s contributions, however, were overlooked by the Nobel committee, an example of institutional discrimination known as the Matilda Effect. Esther Lederberg should also have been recognized for inventing replica plating, an elegant technique that she originated by re-purposing her compact makeup pad as a kind of ink stamp for conveniently transferring bacterial colonies from one petri dish to another. Instead, the credit for the invention is given to her famous husband, or, at best, to Dr. and Mrs. Lederberg. Within a few years of winning the Nobel Prize, Joshua Lederberg divorced his wife, leaving Esther without a laboratory, cut off from research funding, and facing uncertain employment. In response, she created a new social circle made up of artists and musicians, including a new soulmate. She devoted herself to a close-knit musical ensemble, the Mid-Peninsula Recorder Orchestra, an avocation that flourished for over forty years, until the final days of her life.

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American Society for Microbiology

Esther lederberg and the rise of microbial genetics.

Oct. 4, 2023

Scientific Beginnings

Lederberg found a little lambda.

The Nobel Laureate's Wife

And Yet, She Persisted

Out of the shadows.

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Author: Madeline Barron, Ph.D.

The 2024 Clinical Virology Symposium Registration Now Open!

Discover asm membership, get published in an asm journal.

Why Don't We Remember More Trailblazing Women Scientists?

E sther Lederberg is standing on an ornate carpet in Stockholm, wearing a ruched gown and a rather serious expression. It’s an unusual getup for the pioneering scientist, who more often wore a lab coat and a wry grin. But it is also an unusual night. The year is 1958, and Lederberg, 35 years old, has been invited to a tony ceremony in Sweden not as a bacterial geneticist but as a wife. Alongside other spouses, she will look on while three men—her first husband, her mentor and another research partner—are jointly awarded the Nobel Prize, for work connected to her own.

“It’s this group of four people who worked on things,” says Rebecca Ferrell, a biologist who has researched Lederberg’s life. “The three guys get the prize, and she gets to put on gloves and a long gown and watch.”

biotechnology?

Professor Esther Lederberg

Born 18th December, 1922 ( Bronx, New York, United States ) - Died 11th November, 2006

Esther Lederberg was a major pioneer of bacterial genetics. She discovered the lambda phage, a bacterial virus which is widely used as a tool to study gene regulation and genetic recombination. She also invented the replica plating technique, which is used to isolate and analyse bacterial mutants and track antibiotic resistance.

Esther Lederberg, 1950s. Taken while attending Cold Spring Harbor Symposia. (Photo credit: Esther M Zimmer Lederberg Memorial website)

Esther Miriam Lederberg was the oldest of two children born to David Zimmer and Pauline Geller Zimmer. Her father was born in 1896 and grew up in Sereth, Bukowina, a part of the Austro-Hungarian empire. He later settled in United States, where he ran a print shop in the Bronx. Growing up during the Great Depression, Esther remembered having just a piece of bread topped with juice squeezed from a tomato for lunch. She was very close to her grandfather. When he tried unsuccessfully to teach her male cousins Hebrew, she asked him to teach her. This was an unusual request because in the Orthodox Jewish tradition girls were not expected to study Hebrew. Esther learnt the language very quickly, making her grandfather very proud when she did all the Hebrew reading for the Passover seders. In December 1946 Esther married Joshua Lederberg, just five months after Joshua wrote her a letter to ask about her research on Neurospora, a type of mould. Joshua was doing a doctorate at Yale University and she working in the laboratory of George Beadle as part of her master's programme at Stanford University. They remained together until 1966 when they divorced. In 1993, when Esther was 70 years old, she married Matthew Simon, an engineer, whom she met in 1989 shortly after he joined Stanford University. She and Matthew shared a passion for music. Esther had a strong interest in medieval, Renaissance and Baroque music.

Esther attended Evander Child's High School in the Bronx. After graduating from school at the age of 16, she won a scholarship to study at Hunter College, City University of New York. Her initial intention was to study French or literature. She soon switched, however, to biochemistry against the advice of her teachers who felt women struggled to get a career in sciences except in the field of botany. In 1942, at the age of 24, on completing her undergraduate degree, Esther was awarded a distinction, and two years later she won a fellowship to Stanford University to take a master's course in genetics. As the fellowship was not enough to survive on, she supplemented her income by working as a teaching assistant in a laboratory, and obtained free accommodation by washing her landlady's clothes. Sometimes she had so little money she recalled having to eat frogs' legs left over from laboratory dissections. In 1945 Esther spent the summer studying with Cornelius Van Niel at the Hopkins Marine Station at Stanford University. The following year she completed her master's degree. Soon after she moved to the University of Wisconsin to join her husband, Joshua, where she began a doctorate under the supervision of R A Brink. She was supported by a United States Public Health Service Fellowship. Her research focused on the process of genetic mutation in the bacterial species Escherichia coli. She completed her doctorate in 1950.

Early on Esther decided to pursue research-oriented work over the more financially lucrative jobs open to women during the Second World War. This was in part driven by her belief that such jobs would be taken away from women once the war was over. She also recognised that research positions were more open to women and provided greater opportunities to advance her scientific knowledge. Between 1941 and 1942, while pursuing her undergraduate studies, Esther worked as a research assistant for Bernard Ogilvie Doge, a plant pathologist at New York Botanical Garden. He introduced her to the mould Neurospora which she continued to research for a number of years. Following graduation she worked with Alexander Hollaender and Milislav Demerec in the US Public Health Service based in the Carnegie Institute of Washington's Department of Genetics (now Cold Spring Harbor Laboratory). The group were investigating the genetics of bacteria as part of the effort to increase the yield of penicillin, an antibiotic produced by the mould Penicillium notatum. Based on this work she jointly authored a paper with Hollaender outlining the effect of ultraviolet radiation and x-rays on mutation production in Penicillium notatum. Published in 1945, this was Esther's first paper in genetics. In 1944, Esther was hired as a research assistant to the geneticists George W Beadle and Edward Tatum at Stanford University. Her work with them greatly assisted their winning of the Nobel Prize in 1958 for discovering the role of genes in regulating biochemical events in cells. Three years later she joined her husband at the University of Wisconsin as his unpaid research associate. Together they launched experiments to investigate the way bacteria manage to adapt and become resistant to a drug to which they were previously allergic. In aiming to understand how chromosomes behave, they demonstrated for the first time that mutant changes occur so rapidly in bacteria that the process could be be tracked in the laboratory. Although Esther was recognised as outstanding in the laboratory both experimentally and methodologically, she struggled to get a permanent academic position. In part this reflected the wider discrimination against female scientists at the time. She had the further challenge of being married to and collaborating with Joshua who, by virtue of being a man tended to attract greater public attention. Esther's modest nature also did not help. In 1953, when Joshua accepted an award from Eli Lilly and pointed out that she too should have been given it because she had played a pivotal part in his work, she characteristically downplayed her significance, arguing 'there are six or eight people in the background every time someone gets an award’. When Joshua moved to Stanford University as head of genetics, in 1959, Esther was appointed as an untenured research associate professor in department of microbiology and immunology. This happened after she and two other women petitioned the dean of Stanford University's Medical School over the lack of women professors on its faculty. Her appointment was made on the basis that she was willing to accept an untenured post. She was in fact overqualified for the position. Like many other women scientists at Stanford University, Esther continued to struggle for recognition for many years. In 1974, fifteen years later, Stanford University changed her title from Senior Scientist to Adjunct Professor. This still did not give her tenure and was effectively a drop in rank. Her contract was to be renewed on a rolling basis and was dependent on her securing research grants. Esther was subsequently invited by the biochemist Stanley Cohen to become the curator of Stanford University's collection of plasmids, small autonomous self-replicating DNA molecules. Plasmid had first been discovered in the 1940s and Stanford had built up a collection from around the world. In 1976 she was appointed director of Stanford's plasmid Reference Centre. As curator she became a key arbiter in the naming of plasmids and the genes that they carried. She continued as the Centre's curator until 1986.

Achievements

Esther's first major achievement was her discovery of the lambda phage when completing her doctorate in 1950. She spotted it when she observed irregular patterns in a culture with different colonies of the bacteria Escherichia coli K-12 (E-coli), including a strain that had been irradiated with ultraviolet light called W-518. What she noticed was that some of the colonies appeared to be missing some segments. Further investigation revealed that this was due to a latent virus in the E-coli K-12 which had become active in the mutant W-519 strain and was preventing its growth. Subsequently Esther was able to show that the lambda phage behaves differently from other known viruses. Unlike other viruses that multiply rapidly inside a host cell and kill it, the lambda phage integrates its DNA into that of the infected bacteria. This allows the virus to pass on its genetic instructions to produce progeny viruses to new generations of bacteria without destroying the host organism. She established further that the process was helped by a mediator she called 'Fertility Factor F', and that the viral genetic material remained dormant unless the bacterium came under stress. This happened for example when it was deprived of nutrients, at which point it reproduced and destroyed the infected cell. Today the lambda phage is a key tool in molecular biology. In part this is because it can be grown easily in E-coli and it is not pathogenic except in the case of bacteria. It has proven particularly helpful in understanding the transfer of genetic material between bacteria, the mechanisms involved in gene regulation and how pieces of DNA break apart and recombine to make new genes. It also serves as a model to study other viruses with similar behaviour, such as the herpes virus, and is also used as a marker of molecular weights. The phage is also an important tool for genetic engineering. Researchers are also exploring its use in the clinic, deploying the phage to treat bacterial infections. Known as phage therapy, which was first developed in the 1920s, this type of treatment is gaining increasing attention as a possible alternative to antibiotics. In addition to discovering the lambda phage Esther invented the replica plating technique . Devised by her in 1951, this method enables scientists to replicate bacteria colonies on a series of agar plates with exactly the same spatial configuration. Having access to replica bacteria colonies was important for comparing bacterial reactions to environmental changes such as nutrition or temperature. Prior to Esther's invention scientists had tried several methods with little success, including the use of blotting paper, metal brushes with small prongs and even toothpicks. Esther developed what was like a rubber stamp with an ink pad. She attached a square piece of velvet to a piston ring. This was, and still is, first pressed on a Petri dish to get an imprint of the colonies to be copied and then pressed onto another dish. What is vital to the process is the thickness of the pile of the velvet. The surface fibres of the fabric are used like hundreds of tiny inoculating needles to transfer bacteria from hundreds of colonies, each derived from a single bacterium, to a series of agar plates prepared with different ingredients. Each plate has different ingredients added, such as antibiotics or nutrient supplements like amino acids and vitamins. Once the transfer process is complete the replicas are incubated and compared with the original plate. The process helps reveal mutant bacteria incapable of forming colonies in the absence of a specific nutrient. It will also show up bacteria resistant to a specific antibiotic as these will flourish in on the plates with the antibiotic. Esther's replica plating technique provided the first way of proving experimentally that bacteria develop resistance to antibiotics spontaneously. Previously scientists assumed such resistance was always caused by exposure to an antibiotic. In 1956 the Society of Illinois Bacteriologists awarded the Pasteur Award to both Joshua and Esther Lederberg, given in 'recognition of their contribution to microbiology, particularly for their fundamental studies in bacterial genetics. This was the first time the award had ever been given to a team of researchers. Two years later, Joshua received the Nobel Prize for Physiology or Medicine for discovering that bacteria can mate and exchange genes. Much of this could not have been achieved without Esther who was more adept at experimental work than he was. Her isolation of the Lambda phage and her discovery of its genetic replication process, as well as her innovative replica plating technique, were clearly crucial to Joshua's research. This piece was written by Lara Marks, December 2015.

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