Analysis of the bacterial community inhabiting an aerobic thermophilic sequencing batch reactor (AT-SBR) treating swine waste

The microflora of a self-heating aerobic thermophilic sequencing batch reactor (AT-SBR) treating swine waste was investigated by a combination of culture and culture-independent techniques. The temperature increased quickly in the first hours of the treatment cycles and values up to 72degreesC were reached. Denaturing gradient gel electrophoresis of the PCR-amplified V3 region of 16S rDNA (PCR-DGGE) revealed important changes in the bacterial community during 3-day cycles. A clone library was constructed with the near-full-length 16S rDNA amplified from a mixed-liquor sample taken at 60degreesC. Among the 78 non-chimeric clones analysed, 20 species (here defined as clones showing more than 97% sequence homology) were found. In contrast to other culture-independent bacterial analyses of aerobic thermophilic wastewater treatments, species belonging to the Bacilli class were dominant (64%) with Bacillus thermocloacae being the most abundant species (38%). The other Bacilli could not be assigned to a known species. Schineria larvae was the second most abundant species (14%) in the clone library. Four species were also found among the 19 strains isolated, cultivated and identified from samples taken at 40degreesC and 60degreesC. Ten isolates showed high 16S rDNA sequence homology with the dominant bacterium of a composting process that had not been previously isolated.