Collaborative Research: The effects of SUP05 cells and virocells on nitrogen cycling in marine oxygen minimum zones

University Of South Florida, Tampa FL

Investigators

Abstract

Bacteria and the viruses that infect them (phages) play a major role in marine ecosystems. Their host-virus interactions can alter community structure, preserve genetic diversity, and impact nutrient cycling. Up to a third of the bacteria that dominate marine oxygen minimum zones (OMZs) are infected with phages, yet the consequences of the host-virus interactions are unknown. Environmental DNA sequence data suggest that a dominant lineage of OMZ bacteria (SUP05) is comprised of species and subspecies that carry out different steps in marine nitrogen cycling and that these cells are often infected by viruses. The nitrogen cycling capacity of diverse SUP05 cells can drive the accumulation of nitrogen cycle intermediates in the oceans or lead directly to significant nitrogen loss. The outcome may be driven in part by phages, by causing cell death, metabolic rewiring of infected cells (virocells), or through the expression of phage-encoded auxiliary metabolic genes (AMGs). This project is testing the overarching hypothesis that SUP05 populations are comprised of diverse nitrogen respiring cell types and that their interactions with phages can determine the fate of fixed nitrogen. The investigators are studying SUP05 cells and viruses from OMZs to detail their combined effects on nitrogen cycling and loss processes in OMZs. The project is providing graduate and undergraduate students with hands-on collaborative field and laboratory research experiences, with a focus on broadening participation in oceanography. Through local science festivals, open houses, and interactive classroom lessons, K-12 students are learning about OMZs, nitrogen cycling, and viral infection. Results are being presented at national and international conferences and published in peer-reviewed journals, and all sequence and biogeochemical data, as well as new cultures of SUP05 and phage isolates are being made available to the broader scientific community. Up to 25% of the fixed nitrogen in the ocean is lost as gaseous products through denitrification and other microbial processes in OMZs. These regions are also hotspots for nitrous oxide (N2O) production and emission to the atmosphere. While sulfur oxidizing chemoautotrophs from the SUP05 clade of marine bacteria and their viruses are abundant in marine OMZs, the roles of host-virus interactions in biogeochemical processes are largely unknown. This interdisciplinary study is evaluating SUP05 cells and phages in stable OMZ fjord systems using a combination of in situ measurements, DNA and RNA sequencing, and laboratory experiments to link the metabolic activities of SUP05 with the underlying nitrogen transformations they mediate in the ocean. The collective expertise of team members using field approaches to study microbial and viral diversity in nature, cultivation studies to test genomic predictions under controlled laboratory conditions, and isotope analyses to identify the rates and mechanisms underlying microbial nitrogen cycling and loss are being combined to provide new information about the conditions and activities that regulate SUP05 nitrogen cycling and loss in marine OMZs. Ultimately, this multi-faceted approach is filling critical gaps in our understanding of SUP05 cells and phages and how they collectively influence the marine nitrogen cycle. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.