Esther Lederberg, the microbiologist who taught us how to stamp bacteria

Esther Lederberg, the microbiologist who taught us how to stamp bacteria

Throughout history we find women scientists with an exceptional career, but who have not received the recognition they deserve. And although society struggles against this difference, it is interesting to know the lives and experiences of important women scientists to prevent history from repeating itself. Today, in honor of the Women Day, we highlight the case of Esther Lederberg, of which The Guardian newspaper wrote as an obituary “She did pioneering work in genetics, but it was her husband who won a Nobel prize” (1).

But who was Esther Lederberg?

Born in 1922 in New York and daughter of a humble family, Esther won a scholarship to study at Hunter College, University of the City of New York. Her intention was to study languages, but she ended up studying biochemistry, a change totally discouraged by her teachers, who considered that women did not have many opportunities in science. After completing her bachelor’s degree in 1942, she studied a master’s degree in Genetics at Stanford University, where she earned a small salary as an assistant professor of biology, and sometimes she picked the legs of dissecting class frogs for dinner. In 1946 she obtained her master’s degree and married Joshua Lederberg. Esther joined Joshua’s research team at the University of Wisconsin as an associate researcher and obtained a PhD four years later.

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Esther M. Zimmer Lederberg (1950). Esther M. Zimmer Lederberg Memorial Website.

Lambda bacteriophage

The first great discovery of Esther Lederberg was the description of the bacteriophage lambda in 1951. A bacteriophage is a virus that infects certain bacteria, takes advantage of their reserves and can end up causing the death of these. In the case of the bacteriophage lambda, its host is the enterobacteria Escherichia coli. Esther described for the first time the ability of bacteriophages to invade a bacterium and integrate their DNA into the chromosome of the infected cell. Until then the described bacteriophages multiplied rapidly within the bacteria and killed them. But in the case of bacteriophage lambda, the virus remained integrated and the bacteria continued to multiply, transmitting the bacteriophage from generation to generation. Only in adverse situations for the host (lack of nutrients, sudden changes in temperature, etc.) the bacteriophage was activated and induced the production of large amounts of viral particles, which ended with the death of the host bacterium due to breakage of its cell wall. It all started when Esther detected some plates of Escherichia coli from her laboratory in which the colonies of bacteria seemed to be “eaten”. Later studies allowed Esther to understand the two life cycles of the viruses, the lysogenic cycle (incorporation of the genetic material in the infected cell) and the lytic cycle (reproduction of the virus and death of the host cell).


Replica plating

Going back to the bacteria, with their research at the University of Wisconsin, the Lederberg determined that bacteria mutate so quickly that changes can be observed in the laboratory. They demonstrated the existence of spontaneous mutations in bacteria by plating a bacterial culture in Petri dishes with different nutrient conditions or the presence of antibiotics. A colony of bacteria is a set of microorganisms that are generated from the same parent. To check how a specific bacterial colony reacts to different nutrients or antibiotics you need to have genetically equal populations. That is why Esther Lederberg developed the method of “replica plating”:

  • A piece of velvet is put in contact with colonies grown in a Petri dish and the velvet fibers trap some bacteria from the colonies.
  • Next, this piece of velvet is used to “stamp” the bacteria in Petri dishes with different conditions, but in the same location as in the initial plate. So the reference of the origin colony is maintained. If there is an empty space in a plate with a certain antibiotic while in the origin plate there was a colony it means that this colony is not resistant to the tested drug.

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These studies on bacterial genetics capture the attention of the jury of Nobel Prize, who awarded Joshua Lederberg with the Nobel Prize of Physiology and Medicine to in 1958 “for his discoveries concerning genetic recombination and the organization of the genetic material of bacteria” (2). Until then the couple had shared the authorship of their discoveries (3). However, Joshua made no mention of the importance of his wife in the studies for which he received the award. With this recognition the Lederberg moved to Stanford University, where Joshua joined the new department of Genetics as Head of Department, while Esther joined the department of Microbiology and Immunology, with a temporary position as Associate Research Professor. Years later, the couple divorced, and Esther was proposed as curator of the plasmid collection at Stanford University, a position she held until she retired in 1985.






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