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Important Terminology (Lederberg and Lederberg 1953)
Important Terminology (Lederberg and Lederberg 1953)
Lysogenicity: during multiplication of bacteria, there is transmission of virus potentiality without lysis
When tested with a phage, a bacteria culture can be detected as:
Sensitive = lysed
Resistant = not lysed
Lysogenic: carriers of lambda; have capability of initiating lysis of a indicator strain
Immune: nonlysogenic and resistant to lambda
The Discovery
The Discovery
Esther Lederberg isolated lambda (λ) bacteriophage. Lysogenicity was heavily studied in enteric bacteria, and Esther was interested in studying this phenomenon in Escherichia coli (Lederberg 1950).
She found that the E. coli strain K-12 is lysogenic and carried a latent phage (now known as lambda phage) that presents itself when crossed with a sensitive indicator strain. It was exposed when K-12 was crossed with W-518. The cross produced cloudy plaques in the center of EMB agar plates; plaques were due to the presence of λ in K-12 (Lederberg 1950). Around the plaques were yields of lysogenic, lambda-resistant cultures similar to the K-12 parent. These lysogenic W-518 cells were immune to infection and released unaltered phages (Gottesman and Weisberg 2004). A cross between W-1027 and K-12 resulted in establishing a potential locus called V “lambda" (Lederberg 1950).
The discovery of λ provoked key studies by other scientists, which have advanced the field of molecular biology and the understanding of how living organisms function.
Further Exploration (Lederberg and Lederberg 1953)
Further Exploration (Lederberg and Lederberg 1953)
In 1953, together with her first husband, Joshua Lederberg, Esther Lederberg described E. coli and performed various crosses to understand the genetic basis of lysogenicity.
Lysogenic x lysogenic → lysogenic progeny
Sensitive x sensitive → sensitive progeny
Sensitive x lysogenic → sensitive and lysogenic progeny that segregate
Immune crosses were conducted that enabled them to postulate a locus for the latent phage (Lp1) that maintains λ and determines lysogenicity. This locus was found to be linked with Gal4, which is a distinctive marker of W-518.
Additionally, there was an observation of a mutant (λ-2); it lyses lysogenic and sensitive bacteria.
Figure 1. Sensitive, lysogenic, and immune crosses (Lederberg and Lederberg 1953).
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