Award: OCE-1829641

The project was a collaboration between the University of Tennessee, The Ohio State University and Georgia Institute of Technology/The University of Maryland. The main goal of the research was to understand how the millions of viruses in every drop of ocean water interact with the hundreds and thousands of bacteria found in the same volume of ocean. A key goal for the University of Tennessee group was to accomplish this from RNA sequencing data that is presently being broadly collected by researchers around the world. Starting with data generated in the spring of 2018 from the Southern Ocean near Tasmania, the team was able to develop strong linkages between the virus communities in the system and their potential hosts. This was particularly true to a group known as the "giant viruses": these members of the Nucleocytoviricota infect protists that are abundant members of the Southern Ocean community. The observations demonstrated that changes in the availability of the trace element Fe influenced the activity of these viruses. Increases in Fe availability made some more activty while decreases in the availability of Fe made other viruses more active. The results shine a light on how nutrients can indirectly regulate microbial community form and function. The team also completed field expeditions to the Atlantic Ocean in 2019 and 2022. In 2019 a 5 day diel study (i.e., around the clock) sampled several ocean depths every 4 hours. Team member extracted RNA for sequencing as well as small molecules to characterize microbial community changes with the solar day. One major observation was the rediscovery of a region of high oxygen just below the thermocline we have refered to as the subsurface oxygen maximum (SOM). This region receives reduced surface sunlight (~ 1%) while at the same time getting nutrients which are upwelled from below. Our observations suggested that this region is expansive across the Atlantic and that biological activity in it is driven by a subset of the cyanobacteria in the genus Prochlorococcus along with various heterotrophic bacteria. Surprisingly, it appaears that the more rapid activity in this region is driven by increase virus infection of the Prochlorococcus: increased infection leads to faster carbon cycling (as more cyanobacteria lyse) which leads to more heterotrophic bacterial activity. The bacteria respire off the carbon and then recycling ammonium, which in turn enhances the growth rate of the Prochlorococcus. One conclusion from this data is that the SOM is likely strong affected by regional climate, and it could become under threat with predictions of climate change that will alter ocean circulation and stratification. A final significant observation in this region was that the assimilation of phosphorous (P) is like partitioned by different members of the microbial community to different times of day. This observation arose from the diel assessment of microbial community function as observed in the RNA sequencing data. In short, different members of the community seemed tuned to best competing for this limiting resource at different times of day. This suggests very tight regulation of nutrient dynamics across the entire community. Moving forward the data also suggest that changes in circulation and mixing might alter how cells perceived time of day (e.g., by changing the depth cells mix too in the water column they will get different light cues) and thus the physical changes in the water column brought on by a changing climate might have serious complications for the future. Along with the above scientific output, this project trained graduate and undergraduate students in lab and field techniques invcluding the state-of-the-art bioinformatics needed to analyse the billions of RNA sequences generated by this study. Papers have been published and will continue to be published from this work, and our observations have been presented at scientific meetings around the globe. Last Modified: 01/29/2024 Submitted by: StevenWWilhelm