Time-scales modulate optimal lysis-lysogeny decision switches and near-term phage fitness

Temperate phage can initiate lysis or lysogeny after infecting a bacterial host. The genetic switch between lysis and lysogeny is mediated by phage regulatory genes as well as host and environmental factors. Recently, a new class of decision switches was identified in phage of the SPbeta group, mediated by the extracellular release of small, phage-encoded peptides termed arbitrium. Arbitrium peptides can be taken up by bacteria prior to infection, modulating the decision switch in the event of a subsequent phage infection. Increasing concentration of arbitrium increases the chance that a phage infection will lead to lysogeny, rather than lysis. Although prior work has centered on the molecular mechanisms of arbitrium-induced switching, here we focus on how selective pressures impact the benefits of plasticity in switching responses. In this work, we examine the possible advantages of near-term adaptation of communication-based decision switches used by the SPbeta-like group. We combine a nonlinear population model with a control theoretic approach to evaluate the relationship between a putative phage reaction norm (i.e., the probability of lysogeny as a function of arbitrium) and the near-term time horizon. We show the adaptive potential of communication-based lysis-lysogeny responses and find that optimal switching between lysis to lysogeny increases near-term fitness compared to fixed responses. We further find that plastic responses are robust to the inclusion of cellular-level stochasticity. These findings provide a principled basis to explore the long-term evolution of phage-encoded decision systems mediated by extracellular decision-signaling molecules, and the feedback between phage reaction norms and ecological context.