Structuring of bacterial communities by phytoplankton and DOM in the Delaware estuary

Relationships among bacteria, phytoplankton and the dissolved organic matter (DOM) pool have been examined with data on total abundance of bacteria and phytoplankton and on concentrations of organic carbon and nitrogen in the DOM pool. Much less is known about how members of the phytoplankton community and compounds in the DOM pool interact with members of bacterial communities in aquatic systems. In particular, our understanding of the impact of phytoplankton on bacterial communities is largely based on studies showing that a few bacteria have interactions with the phytoplankton class dominating during phytoplankton blooms. We explored bacterial and phytoplankton communities and the DOM pool along the full salinity gradient of the Delaware estuary in August and November over three years by examining bacterial 16S rRNA genes via 454 pyrosequencing, phytoplankton pigments via high performance liquid chromatography, and dissolved organic compounds via ultra-high-resolution mass spectrometry. We used approaches taken from multivariate statistics and community ecology to analyze the bacteria and DOM data and then we combined those results with the data on the phytoplankton and biogeochemical properties in the estuary. The composition of the bacterial and phytoplankton communities and of the DOM pool varied greatly with salinity and month, although less so among the three years, depending on the variable. This variation was used to explore inter-relationships among microbes and dissolved components of the estuary. Our results illustrate the need for new approaches in analyzing complex, inter-related data sets and suggest that the different members of the phytoplankton community and different DOM components have significant relationships with different members of the bacterial community, contributing to the success of some bacteria over others.