Community dynamics of archaea in an estuarine river water column and implications for archaeal biogeochemistry

Abstract

In the past three decades, it has been established that archaea play important biogeochemical roles in the marine water column and sediments, but there remains a gap in knowledge about the phenology of these marine planktic archaea. Even less is known about their phenology and diversity in estuarine environments than in marine environments. Here I report the results of a year-long census of archaeal diversity created by filtering water from the Broadkill River, an estuarine river mouth in Delaware, USA, and sequencing the DNA extracted from filters. These results provide information on how the archaeal community, at the class level, changed over time, as well as based on particulate size fraction, tides, and environmental parameters such as temperature and salinity. The most important factor affecting community composition was particle size, suggesting a partitioning of archaea into particle-associated and free-living groups. Seasonal and tide-based trends, while not important in explaining overall diversity, were evident for several classes of archaea. Of particular interest were Nitrososphaeria (Marine Group I), the relative abundance of which correlated with tide, and Thermoplasmata (Marine Group II), which increased in relative abundance during the warmer months. The dominance of the community by Thermoplasmata during the summer presents an opportunity to investigate this uncultured group’s membrane lipids in the future. Methanogens and other anaerobic archaea were present in greater abundance in the larger size fraction, suggesting the use of anoxic particle interiors and active anaerobic metabolism in the water column.