Particle-Associated Archaea Across a Salinity Gradient in the Tidally Influenced Broadkill River, DE

Particulate matter in marine and aquatic systems has been shown to host microbial communities distinct from the free-living fraction, which is attributed to the concentration of nutrients and the presence of microhabitats within these particles. Some of these microhabitats include anoxic zones within the interior of the particles, allowing the presence of anaerobic microbes. While several studies have explored the bacterial community composition of particulate matter in marine, estuarine, and riverine systems, there have been fewer studies analyzing the archaeal community. As such, the implication of particle-associated anaerobic archaea in an oxygenated water column environment has not been fully explored. We investigated near shore particle-associated archaea to determine the extent to which the potential anaerobic habitat of particles has in allowing global distribution of anaerobic sediment associated archaea. In this study, the archaeal community structure of size-fractioned particles was analyzed for the presence of archaeal groups along a salinity gradient in the tidally influenced Broadkill River. Four freshwater to brackish stations were analyzed as well as one marine station. It was found that members of methanogen groups and the Miscellaneous Crenarchaeota Group were preferentially enriched on larger particles in fresh and brackish river water, but the community at the marine station was consistent between particle sizes with very few members of anaerobic sedimentary groups present. These results suggest that larger particles may have a greater potential for an anaerobic interior habitat and that in addition to salinity, particle composition may be a factor that dictates which archaeal groups can thrive. The presence of anaerobic sedimentary archaeal groups within larger particles also suggests the plausibility for entrained particulate matter as a transport and distribution mechanism for sedimentary archaeal groups throughout the ocean.