Phylogenetic characterization of bromate-reducing microbial community enriched anaerobically from activated sludge

Bromate is a weakly carcinogenic disinfection by-product generated from naturally existing bromide during ozonation. In order to uncover the phylogenetic diversity of bromate-reducing aquatic bacteria, the microbial mixed cultures were enriched anaerobically from various activated sludge samples with a high concentration of 3.6 mmol/L bromate which served as the electron acceptor in batch-fed reactors. Then the phylogenetic diversity was characterized by employing 16S rRNA gene-based clone libraries and high-throughput sequencing. Results showed that as highest as 48.65 mg/L [BrO₃^--Br] (0.61 mmol/L) could be reduced to Br^- within an operational cycle of 48 h, indicating the presence of bromate-reducing bacteria. The microbial analysis based on 16S rRNA gene clone libraries indicated that the dominant bacteria in the enriched consortium were affiliated to the genera of Aeromonas, which had been reported and implied its functional application to reduce bromate. In addition, some other subdivisions of bromate-reducing bacteria were enriched at different operational cycles. The abundance of the genus Rivibacter belonging to Comamonadaceae were increased after 10 cycles enrichment, which might represent another type of novel bromate bio-reducers. The study provided new insights for the phylogenetic diversity of the bromate-reducing microorganisms while further researches are required to verify the bromate bio-reduction mechanism.