The value of information gathering in phage–bacteria warfare

Abstract

Phages—viruses that infect bacteria—have evolved over billions of years to overcome bacterial defenses. Temperate phage, upon infection, can “choose” between two pathways: lysis—in which the phage create multiple new phage particles, which are then liberated by cell lysis, and lysogeny—where the phage’s genetic material is added to the bacterial DNA and transmitted to the bacterial progeny. It was recently discovered that some phages can read information from the environment related to the density of bacteria or the number of nearby infection attempts. Such information may help phage make the right choice between the two pathways. Here, we develop a theoretical model that allows an infecting phage to change its strategy (i.e. the ratio of lysis to lysogeny) depending on an outside signal, and we find the optimal strategy that maximizes phage proliferation. While phages that exploit extra information naturally win in competition against phages with a fixed strategy, there may be costs to information, e.g. as the necessary extra genes may affect the growth rate of a lysogen or the burst size of new phage for the lysis pathway. Surprisingly, even when phages pay a large price for information, they can still maintain an advantage over phages that lack this information, indicating the high benefit of intelligence gathering in phage–bacteria warfare.

Competitive advantages of T-even phage lysis inhibition in response to secondary infection

“…Interestingly, Bacillus subtilis phages from the SP β family were found to alter their lysogenization frequency using a peptide-based communication system, termed arbitrium, produced upon infection, high levels of which promote lysogeny [ 37 – 39 ]. Because both arbitirum and MOI signal similar information in this scenario [ 35 ], we could ask why MOI was not enough; also, we could ask if there is an example in nature where LIN is regulated by an arbitirum-like system, and if not, why.…”