Lysogenic host–virus interactions in SAR11 marine bacteria

Host–virus interactions structure microbial communities, drive biogeochemical cycles and enhance genetic diversity in nature1,2. Hypotheses proposed to explain the range of interactions that mediate these processes often invoke lysogeny3–6, 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 nature6,8–15. Here, we report the discovery of prophages in cultured SAR11, the ocean’s most abundant clade of heterotrophic bacteria16,17. 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. Here, the authors report the discovery of prophages in cultured SAR11 and show that lysogenic SAR11 produce virions by prophage induction of up to 2.3% of infected cells under carbon-replete growth conditions and up to 30.6% of infected cells under carbon-deplete conditions.