Investigating Aquatic Microbial Community Dynamics From Rivers To Oceans Using Molecular Biological Techniques

Aquatic habitats are dominated by microbial life and these microbial communities are responsible for the major biogeochemical cycles within these environments. Using molecular biological techniques we set out to examine the activity and diversity of these microbial communities within a variety of aquatic ecosystems. First, we examined the relative expression of key respiratory genes from plankton metatrancriptomic libraries prepared from samples over an oxygen gradient. These samples demonstrated changes consistent with energetically favorable terminal electron acceptor availability and we show that, rather than abrupt transitions between terminal electron acceptors, there is substantial overlap in time and space of these various anaerobic respiratory processes in Chesapeake Bay. Second, metatranscriptomes of four major Chesapeake Bay tributaries, the Choptank, James, Potomac and Susquehanna Rivers were annotated to characterize active microbial communities within these environments. Annotations for reads mapped to bacterial and archaeal transcripts were highly similar between rivers (~17 ±3% Archaeal and ~83 ± 3% Bacterial). Because nutrient loading from rivers is a major factor driving anoxia and general biological health within Chesapeake Bay, we also examined the relationship between the active microbial communities in the riverine samples to those within the bay. We found that although oxic waters within the Chesapeake Bay vary taxonomically from those within the rivers, functionally these communities are dominated by transcripts related to cell growth, transport and photosynthesis. Finally, we examined viral and bacterial dynamics along a latitudinal transect in the Atlantic Ocean from approximately 10N to 40S. Viral abundance decreased with depth and was highly correlated to bacterial abundance. Viral-size fraction DNA was used to quantify the abundance of two pelagiphages, using pelagiphage-specific primers along this transect. We found that HTVC010P, a member of a podoviridae sub-family, was most abundant in surface waters. HTVC008M, a T4-like myovirus, was present in the deep chlorophyll maximum, although it was not as highly abundant as HTVC010P in surface waters. Interestingly, HTVC008M was only present at a few of the most southern stations, suggesting latitudinal biogeography dynamics of SAR11 phages. Additionally, viral production experiments provide evidence that HTVC008M may be temperate