Trends in Microbiology
ReviewSpecial Issue: Microbial EnduranceWhy Be Temperate: Lessons from Bacteriophage λ
Section snippets
Phage Life Cycles
Some pathogens exploit their host for a very limited amount of time. In humans, for instance, most influenza virus infections last for less than 10 days [1]. The duration of the infection is generally limited by host immunity but it can also be reduced by the death of the infected host. In contrast, other pathogens can remain in their host for a very long time in a latent state. Many human viruses have adopted this alternative life history strategy. For instance, infections by herpes simplex
Latency as a Fixed Strategy
An understanding of the regulation of lysogeny in λ provides invaluable information on the evolution of latency in pathogens. When should pathogens adopt such latent life-history strategies? To answer this question, Berngruber et al. 18, 19 studied the competition between two λ variants with distinct life history strategies. The wild-type temperate λ has a high lysogenisation rate (ϕ ∼ 0.5) and a low induction rate (α ∼ 10−4). In contrast, the virulent λcI857 is a thermosensitive mutant with a low
Latency as a Plastic Strategy
In the above section, latency is assumed to be a fixed strategy. Bacteriophage λ, however, is also known to exhibit plastic life-history strategies. For instance, the efficacy of lysogenisation and the induction rate of the prophage can vary with the environment. These conditional strategies are well studied on a molecular level but the adaptive nature of this plasticity is often overlooked.
Concluding Remarks
The discovery and the characterization of bacteriophage λ has led to major discoveries in molecular biology [14]. In particular, the regulation of the lysis–lysogeny decision remains a very fruitful topic that stimulated a broad range of research studies 26, 37. The molecular details of the genetic switch of λ have been scrutinized for decades and led to a deep understanding of gene regulation that shed light on many other biological regulatory processes. The lysis–lysogeny decision has
Acknowledgments
This work benefited a lot from discussions with Thomas Berngruber, Marc Choisy, Troy Day, Bryan Grenfell, Quentin Legros, Bruce Levin, Sébastien Lion, Ana Rivero, and Joshua Weitz.
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