The interplay between the marine diazotroph <i>Vibrio diazotrophicus</i> and its prophage shapes both biofilm structure and nitrogen release

Diazotrophs are key players in ocean functioning by providing fixed nitrogen to ecosystems and fueling primary production. However, from a physiological point of view, the active release of nitrogenous compounds by diazotrophs is paradoxical, since they would invest in an energy-intensive process and supply nutrient to non-sibling cells, with the risk of being outcompeted. Therefore, alternative ways leading to the release of fixed nitrogen must exist. Here, we show that the marine non-cyanobacterial diazotroph <i>Vibrio diazotrophicus</i> possesses one prophage, whose activation leads to cell death, increased biofilm production, and the release of dissolved organic compounds and ammonium. Taken together, our results provide evidence that marine phage-diazotroph interplay leads to the creation of microhabitats suitable for diazotrophy, such as biofilm, and to nutrient cycling, and contributes to better understanding of the role of viruses in marine ecosystems.