Print PagePhytoplankton community succession has been identified as a potentially important driver of lake bacterial community dynamics during summer stratification. Our objective was to determine if correlative bacterial and phytoplankton community patterns documented in humic lakes could be attributed to the effect of phytoplankton on bacterial communities. If phytoplankton species influence bacterial community composition by enriching for certain bacterial taxa, then bacteria responsive to particular phytoplankton are expected to (i) increase in abundance when incubated with phytoplankton assemblages containing the specified phytoplankton species and (ii) exhibit correlated seasonal patterns of abundance with that phytoplankton species. Bacterial communities from three humic lakes were incubated with phytoplankton assemblages from the same three lakes or a no-phytoplankton control in a full factorial mesocosm experiment (n=3) incubated in situ for 7 days. Bacterial communities from before and after incubation were characterized using ARISA community fingerprinting and DNA sequencing of 16S small subunit rRNA genes. Bacteria differentially enriched in phytoplankton treatments versus no-phytoplankton controls were compared against a database of bacteria in our study lakes that have exhibited correlated seasonal patterns of abundance with individual phytoplankton species as detected by local similarity analysis.
Results/Conclusions
Correspondence analysis results indicate that over the incubation period, bacterial communities shifted to reflect the phytoplankton assemblage with which they were incubated. A number of bacterial genera increased over the incubation period in a subset of phytoplankton-containing mesocosms and decreased in corresponding no-phytoplankton controls. Sixteen bacterial taxa were both correlated with specific phytoplankton populations in the environment and enriched in phytoplankton treatments relative to no-phytoplankton controls. These observations provide evidence to support the hypothesis that changes in the phytoplankton community induce corresponding shifts in bacterial community composition. The mechanism for phytoplankton influence on bacterial communities appears to be a taxon-specific response of bacteria to different phytoplankton species, potentially due to phytoplankton release of species-specific combinations of exudates. In aquatic systems, characterization of phytoplankton community patterns may be important for determining the contribution of additional forces influencing bacterial community dynamics.
