Prophage-encoded chitinase gene supports growth of its bacterial host isolated from deep-sea sediments

Auxiliary metabolic genes encoded by bacteriophages can influence host metabolic function during infection. In temperate phages, auxiliary metabolic genes (AMGs) may increase host fitness when integrated as prophages into the host genome. However, little is known about the contribution of prophage-encoded AMGs to host metabolic properties. In this study, we examined a temperate bacteriophage, and its piezotolerant Pseudomonas sp. host obtained from sediment samples collected from the Kermadec Trench at ~10 000 m water depth. Both the phage and host were present throughout the sediment profiles from the surface to 30 cm into the sediment, covering large gradients of environmental conditions. The host and phage each carried one chitinase gene, which differed from each other, suggesting that chitin degradation plays a role in their substrate supply. We demonstrated that prophage-encoded chitinase supported host chitin degradation and growth in the presence of chitin. Furthermore, prophage induction dynamics were strongly substrate-dependent, suggesting that the host controls the lysis-lysogeny switch in response to the presence of chitin, thus optimizing the trade-off between the loss of cells from prophage induction and prophage enhancement of host performance. Overall, the results demonstrate prophage-encoded AMGs as collaborative goods for their hosts and emphasize the potential role of phage-host interactions in benthic biogeochemical cycling, as well as for the capability of deep-sea bacteria to efficiently adapt and thrive at a wide range of environmental conditions.