Genetic changes in the bacterial community structure associated with protistan grazers

Besides controlling bacterial production, bacterivorous protists are though t to govern bacterial community structure. Experimental work has shown that both grazers and bacteria developed strategies that may influence the bact erial community structure. However, evidence from the natural environment i s still lacking. Advances in molecular techniques now allow the profiling o f natural bacterial assemblages. We used denaturing gradient gel electropho resis (DGGE) to profile a bacterial community in a continuous flow system t hat was fed with living and detrital cyanobacterial cells. Although attempt s were made to remove eukaryotic grazers, heterotrophic nanoflagellates wer e growing in the second stages of the system. Analysis of DGGE patterns by nonmetric multidimensional scaling showed a large change in the bacterial c ommunity structure coinciding with the peak in protist numbers. Our results show that DGGE analysis can be used to facilitate studies on the effect of protistan grazing on natural bacterial communities.