COMMUNITY STRUCTURE OF A MICROBIAL MAT - THE PHYLOGENETIC DIMENSION

Traditional studies of microbial communities are incomplete because of the inability to identify and quantify all contributing populations. In the present study, we directly determine the abundance and distribu tion of sulfate-reducing bacterial populations in a microbial mat comm unity by using hybridization probes complementary to the 16S-like rRNA s of major phylogenetic groups. Most of the major groups were found in this single community, distributed for the most part in nonoverlappin g depth intervals of the mat. The reflection of the phylogenetic struc ture in the community structure suggests that those species making up the major phylogenetic groups perform specific interrelated metabolic functions in the community. Comparison of population profiles to previ ously observed rates of sulfate reduction suggests there are additiona l populations of sulfate-reducing bacteria both within the photooxic z one and deeper in the mat.