Joshua Lederberg and genetics of bacteria


Joshua Lederberg (1925-2008), along with Edward Tatum, were the discoverers of the phenomenon of bacterial conjugation. With that, they opened the doors of genetic bacteria, organisms from which they doubted were suitable for genetic analysis.

Until 1940, many bacteriologists assumed that the bacteria did not follow the rules of inheritance discovered in plants and animals, but they were able to adapt to the environment through direct methods, more Lamarckian than anything else. It is therefore doubted that the bacteria may have genes. If you submit a bacterial culture to an antibiotic, slowly they appear resistant until all culture bacteria become resistant to the antibiotic. However, the Luria-Delbrück experiment shows that inheritance in bacteria is Darwinian, no different from the rest of organisms.

Could the bacteria have some kind of sex? Lederberg meant yes, and performing a risky experiment, with little hope of success, mixed the cultures of bacteria that differed to each other in phenotypes needed to grow some chemicals. Using the prototrophic selection, spreading the mixture in culture media where bacteria must synthesize all compounds in order to grow, bacteria could find that had “liberated” the need for these compounds. Clearly that the original bacteria had mixed their genes and created new bacteria without these requirements, a phenomenon that was dubbed conjugation. It was also clear that bacteria were haploid, that is, they only have one copy of each of its genes, unlike plants and animals, which have two copies.


Lederberg is experiment was a mixture of perseverance, wit and luck. Today we know that only some strains of bacteria can spread genes by conjugation, thanks to the presence of plasmids responsible. With the discovery of the conjugation, the doors opened to Bacterial Genetics, allowed the growth of billions of organisms in a short time, and easily keep in the laboratory.

Lederberg and Tatum, along with George Beadle, received the Nobel Prize for Medicine in 1958 “for their discoveries concerning genetic recombination and the organization of the genetic material of bacteria”. Lederberg, according to the Academy, earned half the prize. In addition to conjugation, transduction and the discovering plasmids, being also the inventor of those words. Later, he started working for Space Agency (NASA) programs extraterrestrial life, exobiology and artificial intelligence, without abandoning his research on molecular and bacterial genetics.