Nutritional Status Regulates Bacteria‐Virus Interactions in the Northern South China Sea.

Heterotrophic bacteria play a vital role in the marine carbon cycle and viruses are an important regulator of bacterial metabolism and community composition. It remains unclear about how bacteria‐virus interactions vary with environmental conditions in oceans. In this study, bacterial metabolic activity and community composition were examined in three treatments with different viral pressure (control, virus‐rich and virus‐reduced) through bioassay experiments at three stations with different environmental conditions in the shelf of the northern South China Sea. Our results showed that bacteria‐virus interactions varied with environmental conditions. Viral lysis mediated bacterial growth rate (BGR) and production by shaping bacterial community composition. Furthermore, the effect of viral lysis on bacterial growth rate and production was reduced in substrate‐rich waters compared to substrate‐low waters. However, the opposite pattern occurred for viral regulation on bacterial respiration and carbon demand, likely since viral lysis dramatically mitigated the maintenance respiration of bacteria. Consequently, viral lysis to greater extent mitigated bacterial carbon processing in substrate‐rich environments than in substrate‐low environments. Our findings provided new insights into bacteria‐virus interactions, and improved our understanding of the role microbial processes in carbon cycling in oceans. Plain Language Summary: Heterotrophic bacteria play important roles in marine biogeochemical cycle and their viruses manipulate these processes. We found that viral regulation of bacterial metabolism varied with environmental conditions and the two aspects of bacterial metabolism responded differently to viral lysis. The reductions of bacterial growth rate and production caused by viral lysis increased from nearshore to offshore seawaters, while viral regulations on bacterial respiration and carbon demand showed the opposite pattern. The reasons for differences in the regulation of bacterial metabolism by virus varied with environmental conditions may be that high substrate supply in nearshore waters improved antiviral defense and dramatically mitigated the maintenance respiration of bacteria. In general, viral lysis to greater extent mitigated bacterial carbon processing in substrate‐rich environments than in substrate‐low environments. Our study provided new insights into the interactions of bacterial metabolism with viruses, and improved our understanding of marine carbon cycle in contrasting trophic environments. Key Points: Viral lysis reduced bacterial growth rate and production less in the substrate‐rich waters than oligotrophic watersVirus‐induced losses in bacterial respiration and carbon demand decreased offshoreViral lysis mitigated bacterial carbon processing more in substrate‐rich environments than in oligotrophic environments [ABSTRACT FROM AUTHOR]