STIMULATION OF AQUATIC BACTERIAL-ACTIVITY BY CYANOBACTERIA

The time-course response of natural bacterial populations and isolates from lake water to various densities of the filamentous cyanobacteria Aphanizomenon flos-aquae and Lyngbya birgei collected from the same l ake is reported. The cyanobacteria were separated from the bacteria by dialysis membranes that allowed only dissolved cyanobacterial product s to pass. Bacterial H-3-thymidine incorporation and cell number were significantly (p<0.05) correlated with cyanobacterial density for both species. Estimated dissolved organic carbon (DOC) utilization, based on bacterial biomass changes over time, were usually significantly (p < 0.0 1) correlated with cyanobacterial density and the decrease in bu lk pool DOC for both species. Bacterial volume per cell increased sign ificantly (p < 0.05) in response to cyanobacterial density on day 5 of the experiments; cell volume remained unchanged on day 1. Bacterial. cell numbers on outer surfaces of the tubular membrane containing the cyanobacteria (on the side exposed to the test bacteria) were signific antly (p < 0.01) correlated with cyanobacterial density. Statistical a nalysis inferred that bacteria closely associated with cyanobacteria ( i.e. attached) responded more strongly to cyanobacterial products than free-living bacteria. Overall, our results indicate that cyanobacteri al products have a potentially important role in regulating bacteriopl ankton productivity in aquatic systems.