Abstract
A novel sewage treatment system consisting of an anaerobic Upflow Anaerobic Sludge Blanket (UASB) reactor and an aerobic biofilter reactor was operated continuously for over 400 days with raw domestic sewage as a feed. Sulfate-reducing bacteria plays an important role in Biochemical Oxygen Demand (BOD) degradation in the UASB reactor especially during winter when the operational temperature is low. In this study, the diversity of adenosine-5'-phosphosulfate reductase (apsA) genes, which produce a key enzyme for sulfate respiration and are present in all sulfate-respiring prokaryotes (SRPs), in UASB sludge was analyzed by cloning and sequencing techniques. The apsA amino acid sequence-based phylogenetic tree showed that the identified clones belonged to four groups: the sulfate-reducing bacterial group, Syntrophobacteraceae, Thiobacillus and the clone cluster group, distantly related to any previously described apsA clone. The amino acid sequence of the unknown apsA clones has a high homology to those of SRPs. Real-time PCR quantification which used the primer sets specific for each of the four apsA gene sequences revealed that Desulfobulbaceae and Desulfovibrionales were the predominant species all of the sulfate-reducing bacteria in the UASB sludge throughout the experimental period. An excellent correlation of apsA gene abundance and behavior was found between the sulfate-reducing bacteria and Thiobacillus, as well as between Syntrophobacteraceae and the unknown apsA clone group. However, cells having the unknown apsA gene in the UASB sludge could not be identified.
