Esther Miriam Zimmer Lederberg (December 18, 1922 – November 11, 2006) was an American microbiologist and a pioneer of bacterial genetics.

Lederberg also founded and directed the now-defunct Plasmid Reference Center at Stanford University, where she maintained, named, and distributed plasmids of many types, including those coding for antibiotic resistance, heavy metal resistance, virulence, conjugation, colicins, transposons, and other unknown factors.

Esther Miriam Zimmer was the first of two children born in the Bronx, New York, to a family of Orthodox Jewish background.

[5] In 1944 she won a fellowship to Stanford University, working as an assistant to George Wells Beadle and Edward Tatum.

[2] She later traveled west to California, and after a summer studying at Stanford University's Hopkins Marine Station under Cornelius Van Niel, she entered a master's program in genetics.

[11] In 1956, Esther and Joshua Lederberg were honored for their fundamental studies of bacterial genetics by the Society of Illinois Bacteriologists, which awarded them the Pasteur Medal.

She initially reported the discovery in 1951 while she was a PhD student and later provided a detailed description in a 1953 paper in the journal Genetics.

[13][15] Esther and Joshua Lederberg demonstrated that λ, in its quiescent form, genetically mapped near the E. coli genes required for metabolism of the sugar galactose (gal).

The Lederbergs proposed that the genetic material of λ physically integrated into the chromosome next to the gal genes and subsequently replicated as a prophage along with the DNA of the host bacterium.

In 1957, Lederberg gave a talk on λ lysogeny and specialized transduction at the Symposium of Bacterial and Viral Genetics in Canberra, Australia.

[18][2] In 1958, she presented her findings on the fine-structure mapping of the gal locus at the 10th International Congress of Genetics in Montreal, Canada.

When some of the crosses failed to give rise to recombinants, she suspected that some of her E. coli strains had lost a "fertility factor.

The DNA sequence encoding the F factor can exist either as an independent plasmid or integrate into the bacterial cell's chromosome.

[21] Biographer Rebecca Ferrell believes that the method Lederberg invented was likely inspired by using her father's press at his work, pressing a plate of bacterial colonies onto sterile velvet, after which they were stamped onto plates of media with different ingredients, depending on the desired traits the researcher wished to observed.

[2] The Lederbergs used the replica-plating method to demonstrate that bacteriophage- and antibiotic-resistance mutants arose in the absence of phages or antibiotics.

Instead, the delay hurt her legacy as an independent research scientist, and her findings on bacterial sex are now credited primarily to her husband.

[12] The lack of credit Esther Lederberg is given for development of the replica plating technique has been cited as an example of the Matilda effect, in which discoveries made by women scientists are unfairly attributed to their male colleagues.

[32] As Luigi Luca Cavalli-Sforza later wrote, "Dr. Esther Lederberg has enjoyed the privilege of working with a very famous husband.

When the couple attended the 1951 Cold Spring Harbor Symposium, he discussed Esther's doctoral work on E. coli and acknowledged her as second author.

[2] Ferrell notes, however, that he did not later acknowledge her work when he wrote an autobiographical account of their discovery of genetic recombination in bacteria.

[35] Later in 1974 as a senior scientist, she was forced to transition to a position as adjunct professor of medical microbiology, which was effectively a demotion.