Linking viral production to bacteria mortality and carbon cycling in the oligotrophic Pacific ocean

Abstract

Viruses are now a popular significant component of marine ecosystems and recognized as crucial contributors to elemental cycling within the microbial loop. While early study on viral community dynamics paid more focus on coastal environments, resulting in an underrepresentation of open ocean study. In this research, we measured the rates of viral production (VP) and assessed the viral processes from the surface to the deep sea (500 m), comparing bacterial losses due to viral lysis across depth. In summary, VP in surface water was ranged between 0.11 and 0.15 x 106 viruses mL- 1 h- 1, while at the deep chlorophyll maximum (DCM) layer, it varied from 0.08 to 0.22 x 106 viruses mL- 1 h- 1. The lowest rates of VP were found at a depth of 200 m ranging from 0.06 to 0.08 x 106 viruses mL- 1 h- 1. Our findings may also aid in elucidating the role of virus-mediated mortality (VMM) in bacterial populations. It is important to note that there was an increase in VMM from the surface to the deeper layers of the water column. We propose that the elevated viral mortality rates of bacteria in deeper aquatic environments correspond with the reduced grazing rates on bacteria by protists in these regions. Based on the estimation, we found about 49-60% at surface and 87-100% of bacterial production at the DCM layers organic matter released by virus lysing bacteria cells into dissolved organic carbon pools. This suggests that viral lysis may account for a substantial portion of the carbon demand for bacterial populations.