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The Bacteriophage’s gambit
Game theory is defined as strategies that account for the actions of other players. If the term is familiar to you, then you’ve probably heard of the most famous example. Devised by Merrill Flood and Melvin Dresher is “The Prisoner’s Dilemma” which highlights that neither extreme cooperation nor competition are realistically favourable in a particular scenario. Game theory’s application is broad as it can be found in social, economic, and computer sciences.
Game theory applies beautifully to bacteriophage (viruses that hijack bacteria specifically) behaviour – demonstrated in a recent article published by Aframian, Bendori, et al. λ-bacteriophages, which attack the bacteria Bacillus subtilis, have two stages. A lytic stage, where newly replicated bacteriophages burst through B. subtilis ready to infect another set of bacteria, is its “active” state. Conversely, they can be in a dormant or lysogenic state where the bacteriophage hijacks the B. subtilis genomic machinery to prepare replicating themselves, but otherwise do not damage the structural integrity of the host.
The novel elements of Aframian, Bendori, et al. ‘s research highlights that λ-bacteriophages determine which state to enter by employing arbitrium peptides, a protein produced by bacteriophages, in a small molecule communication system. The authors were able to infer the different components of the model by using a variety of strains with genetic knockouts of each component of the signalling pathway.
They observed an interesting phenomenon. When bacteriophages infect B. subtilis and enter a lysogenic state, they activate aimP which results in a steady stream of abitrium peptide into the environment. If there is a high enough concentration of aimP peptides, other bacteriophages suppress induction to the lytic stage even if the cell is experiencing DNA damage. Moreover, bacteriophages are extremely sensitive to the concentration of aimP.
Why would λ-bacteriophages not lyse a cell that is about to be destroyed? Because the competition is too fierce, according to the authors. Bacteria tend to cluster in dense spatially clustered communities. If all bacteriophages were to enter the lytic state- there wouldn’t be many options in terms of new healthy hosts for them to infect.
Bacteriophages would rather hedge their bets and allow their hosts to survive just a bit longer until their situation is more to their liking. This is unusual as viruses are not considered a living entity. Nevertheless, their genetic data and subsequent capabilities enable them to make the best of their situation.
Link to the original post: Aframian, N., Omer Bendori, S., Kabel, S. et al. Dormant phages communicate via arbitrium to control exit from lysogeny. Nat Microbiol 7, 145–153 (2022). https://doi.org/10.1038/s41564-021-01008-5
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