Microorganisms in Lake Erie are primary agents that drive the cycling of essential nutrients, such as carbon, nitrogen and phosphorus; therefore, their diversity and dynamics holds great implications for the function and health of Lake Erie ecosystem. However, ecological studies on microbes in Lake Erie have been mostly focused on toxin-producing cyanobacteria Microcystis and related genes. Knowledge on the rest majority of microbes is extremely limited. In our first attempt to characterize Lake Erie microbial community, we pyrosequenced the V6 region of 16S rDNA contents of the free-living (defined as cells that can pass 3.0 µm-pore-size filters) and particle-associated (defined as cells that can be collected on 3.0 µm-pore-size filters) microbial plankton in surface water samples collected from six stations in the western basin of Lake Erie in summer 2009. A comprehensive hydrology and nutrient chemistry survey of the water samples was also conducted to measure the temperature, pH, dissolved oxygen (DO), turbidity, and concentrations of chlorophyll a, dissolved organic carbon (DOC), organic nitrogen (DON) inorganic nitrogen (nitrate and ammonium), phosphate (Pi), soluble reactive phosphate (SRP). Statistic analysis was performed to discern a pattern of bacterial community structure based on measured environmental parameters.

Results/Conclusions

A total of 20,000 16S rDNA V6 region sequences, i.e., average 1600 sequences in each of the 12 pyrosequence libraries, were obtained. Recovered 16S rDNA sequences were affiliated with bacteria and archaea across a total of 27 phyla and 98 orders. Particle-associated bacteria showed a clear distribution pattern along the nitrogen supply (DON + nitrate) and DO gradient. They were predominantly members of cyanobacteria (~60% in average) and Burkholeriales (betaproteobacteria, ~7%) in the three eutrophic stations that are near and within the Sandusky Bay. In the three stations with lower N supply and distant from Sandusky Bay, they composed more diversely, with Bacteroidales (bacteroidetes, ~15%), Actinomycetales (actinobacteria, ~7%) and Burkholeriales (~7%) as major taxa. In contrast, no significant correlation was found between the taxonomic structure of free-living prokaryotic plankton and any of the hydrological and chemical parameters. Our result suggested that, in the western basin of Lake Erie, nutrient supply and dissolved oxygen level may play a significant role in shaping the taxonomic structure of particle-associated prokaryotic plankton; their effect on free-living cells, however, was not clear. Our result also suggested that member exchange between the particle-associated and free-living prokaryotic plankton in studied water samples was minimal.