PHYLOGENETIC DIVERSITY OF MESOPHILIC AND THERMOPHILIC GRANULAR SLUDGES DETERMINED BY 16S RIBOSOMAL-RNA GENE ANALYSIS

The microbial diversity of two types of methanogenic granular sludge, mesophilic (35 degrees C) and thermophilic (55 degrees C), which had b een treating sucrose/propionate/acetate-based artificial wastewater we re compared. 16S rDNA clone libraries were constructed by PCR with a p rokaryote-specific primer set, and partial sequencing of the clonal 16 S rDNAs was conducted for phylogenetic analysis. Of 115 mesophilic gra nule and 110 thermophilic granule clones sequenced, 19 and 22%, respec tively, were phylogenetically affiliated with the domain Archaea, and the remainder in each case were assigned to the domain Bacteria. Withi n the domain Archaea, the 16S rDNA crones in both libraries showed rel atively close relationships with those of methanogens. Within the Bact eria, a major group represented in the mesophilic clone library was th e delta subclass of the Proteobacteria (27%), in which high degrees of relatedness were observed between the clonal 16S rDNA sequences and t hose of previously identified syntrophic bacteria and sulfate-reducing bacteria. In contrast, in the thermophilic clone library, the Thermod esulfovibrio group (19%), the green non-sulfur bacteria (18%) and the low G+C subclass of the Gram-positive bacteria (18%) were predominant. A significant difference between the two libraries was that no clone affiliated with the Proteobacteria was detected in the thermophilic cl one library, whereas the Proteobacteria was the most predominant group in the mesophilic clones. Thirty-six and 24 different sequences were found in the mesophilic and thermophilic clones, respectively, suggest ing that the microbial diversity of the thermophilic granule was lower than that of the mesophilic granule.