Lysogenic host-virus interactions in SAR11 marine bacteria

Host-virus interactions structure microbial communities, drive biogeochemical cycles and enhance genetic diversity in nature^1,2. Hypotheses proposed to explain the range of interactions that mediate these processes often invoke lysogeny^3-6, a latent infection strategy used by temperate bacterial viruses to replicate in host cells until an induction event triggers the production and lytic release of free viruses. Most cultured bacteria harbour temperate viruses in their genomes (prophage)⁷. The absence of prophages in cultures of the dominant lineages of marine bacteria has contributed to an ongoing debate over the ecological significance of lysogeny and other viral life strategies in nature^6,8-15. Here, we report the discovery of prophages in cultured SAR11, the ocean's most abundant clade of heterotrophic bacteria^16,17. We show the concurrent production of cells and viruses, with enhanced virus production under carbon-limiting growth conditions. Evidence that related prophages are broadly distributed in the oceans suggests that similar interactions have contributed to the evolutionary success of SAR11 in nutrient-limited systems.