Host life-history traits influence the distribution of prophages and the genes they carry.

Bacterial strains with a short minimal doubling time-'fast-growing' hosts-are more likely to contain prophages than their slow-growing counterparts. Pathogenic bacterial species are likewise more likely to carry prophages. We develop a bioinformatics pipeline to examine the distribution of prophages in fast- and slow-growing lysogens, and pathogenic and non-pathogenic lysogens, analysing both prophage length and gene content for each class. By fitting these results to a mathematical model of the evolutionary forces acting on prophages, we predict whether the observed differences can be attributed to different rates of lysogeny among the host classes, or other evolutionary pressures. We also test for significant differences in gene content among prophages, identifying genes that are preferentially lost or maintained in each class. We find that fast-growing hosts and pathogens have a greater fraction of full-length prophages, and our analysis predicts that induction rates are significantly reduced in slow-growing hosts and non-pathogenic hosts. Consistent with previous results, we find that several proteins involved in the packaging of new phage particles and lysis are preferentially lost in cryptic prophages. This article is part of the theme issue 'The secret lives of microbial mobile genetic elements'.