An optimal lysis time maximizes bacteriophage fitness in quasi-continuous culture

Abstract

Optimality models have a checkered history in evolutionary biology. While optimality models have been successful in providing valuable insight into the evolution of a wide variety of biological traits, a common objection is that optimality models are overly simplistic and ignore organismal genetics. We revisit evolutionary optimization in the context of a major bacteriophage life history trait, lysis time. Lysis time refers to the period spanning phage infection of a host cell and its lysis, whereupon phage progeny are released. Lysis time, therefore, directly determines phage fecundity assuming progeny assembly rate is maximized. Noting that previous tests of lysis time optimality rely on batch culture, we implemented a quasi-continuous culture system to observe productivity of a panel of isogenic phage {lambda} mutants differing in lysis time. We report that {lambda} phage productivity in our experiments is maximized around an optimal lysis time of 63 min, which is the lysis time of the {lambda} "wildtype" strain. We discuss this finding in light of recent results that lysis time variation is also minimized in the {lambda} "wildtype" strain.