Bacterial Genetics

Joshua Lederberg was impressed by Avery, McLeod, and McCarty’s 1944 study showing that DNA was the critical carrier of genetic information. But many biologists questioned whether the results of genetic studies in bacteria were transferable to more complex organisms. Nevertheless, studying bacteria had a number of advantages: they were simple to grow in inexpensive culture media; they generated rapidly, reducing experiment time; they were easily handled; and they had a simple cell structure.

Animal and plant parents transfer genetic information to their offspring by the process of vertical gene transfer. Bacteria primarily reproduce by dividing into two genetically identical daughter cells (binary fission). Scientists long believed that bacteria were primitive and not suitable for genetic analysis. In 1946, Joshua Lederberg and his major advisor Edward Tatum at Yale University showed that, in bacteria, genetic material is transmitted between two organisms that are not parent and offspring by the process of gene recombination—later termed horizontal gene transfer (HGT). In recognition, thirty-three-year-old Lederberg and Tatum were co-recipients of the 1958 Nobel Prize. Subsequent studies have shown that HGT is common even in very distantly related bacteria and is a mechanism in bacterial evolution. It also underlies the development of drug resistance to antibiotics: when one bacterial cell acquires drug resistance, it can rapidly transfer the resistant genes to many other species.

Salmonella (shown) can cause severe food poisoning, and some bacterial strains are resistant to multiple antimicrobial drugs. Mechanisms leading to resistance mostly involve genes located on plasmids that are easily transferred among Salmonella and other bacteria.

There are three major modes by which HGT can spread genes between members of the same or different bacterial species: bacteria-to-bacteria transfer (conjugation), shown by Lederberg and Tatum (1946); virus (bacteriophage)-to-bacteria transfer (transduction, 1950), which has led to genetic engineering work by Lederberg and his wife Esther Zimmer Lederberg, herself a prominent bacterial geneticist; and the free transfer of DNA (transformation). Lederberg was the leading force in microbial genetics, a founder of molecular biology, a visionary in artificial intelligence, and a spokesperson against the dangers of microbial contamination during space exploration.