Genetic changes in the bacterial community structure associated with protistan grazers

Abstract

Besides controlling bacterial production, bacterivorous protists are thought to govern bacterial community structure. Experimental work has shown that both grazers and bacteria developed strategies that may influence the bacterial community structure. However, evidence from the natural environment is still lacking. Advances in molecular techniques now allow the profiling of natural bacterial assemblages. We used denaturing gradient gel electrophoresis (DGGE) to profile a bacterial community in a continuous flow system that was fed with living and detrital cyanobacterial cells. Although attempts were made to remove eukaryotic grazers, heterotrophic nanoflagellates were growing in the second stages of the system. Analysis of DGGE patterns by nonmetric multidimensional scaling showed a large change in the bacterial community 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. [KEYWORDS: GRADIENT GEL-ELECTROPHORESIS; GRAZING-RESISTANT BACTERIA; 16S RIBOSOMAL-RNA; FRESH-WATER; DIVIDING CELLS; LAKE; BACTERIOPLANKTON; POPULATIONS; ASSEMBLAGES; PROTOZOA]