CHARACTERIZATION OF MICROBIAL COMMUNITIES IN ANAEROBIC BIOREACTORS USING MOLECULAR PROBES

The microbial community structure of twenty-one single-phase and one t wo-phase full-scale anaerobic sewage sludge digesters was evaluated us ing oligonucleotide probes complementary to conserved tracts of the 16 S rRNAs of phylogenetically defined groups of methanogens and sulfate- reducing bacteria. These probe results were interpreted in combination with results from traditional chemical analyses and metabolic activit y assays. It was determined that methanogens in ''healthy'' mesophilic , single-phase sewage sludge digesters accounted for approximately 8-1 2% of the total community and that Methanosarcinales and Methanomicrob iales constituted the majority of the total methanogen population. Met hanobacteriales and Methanococcales played a relatively minor role in the digesters: Phylogenetic groups of mesophilic, Gram-negative sulfat e-reducing bacteria were consistently present at significant levels: D esulfovibrio and Desulfobulbus spp. were the dominant sulfate-reducing populations, Desulfobacter and Desulfobacterium spp. were present at lower levels, and Desulfosarcina, Desulfococcus, and Desulfobotulus sp p. were absent. Sulfate reduction by one or more of these populations played a significant role in all digesters evaluated in this study. In addition, sulfate-reducing bacteria played a role in favoring methano genesis by providing their substrates. The analysis of the two-phase d igester indicated that true phase separation was not accomplished: sig nificant levels of active methanogens were present in the first phase. It was determined that the dominant populations in the second phase w ere different from those in the single-phase digesters.