Effect of low pH and metal content on microbial community structure in an anaerobic sequencing batch reactor treating acid mine drainage

Biological treatments based on sulfate reduction are an alternative to those chemical processes used to control the environmental effects of acid mine drainage. To improve bioreactor performance, an investigation on microbial community composition, to predict the functional role of microorganisms during the treatment, became relevant. Thus, the aim of this study was to evaluate microbial community changes in an anaerobic sequencing batch reactor (ASBR) treating synthetic acid mine drainage under low pH (phases 1 and 2), after addition of metals (phases 3-5), and after an elevation of sulfate concentration from 500 to 1500 mg/L in the absence of supplied nutrients (phase 6). Denaturing gradient gel electrophoresis (DGGE) and pyrosequencing analyses were used to characterize communities. DGGE analyses showed that metals affected the community structure more than pH reduction based on the DGGE analysis and derived dendograms of amplified bacterial 16S rRNA gene fragments, it was seen that the population composition's similarity to the original inoculum was 62% after Fe2+, Zn2+, and Cu2+ addition, and 87% after a pH reduction from 5 to 4. Syntrophobacter, a sulfate-reducing bacterium (SRB), and Methanosaeta, an acetoclastic methanogen, were the most frequently encountered species in the ASBR, with relative SRB group abundances of 8% and 7%, and methanogen group abundances of 8% and 14% in phases 5 and 6, respectively. Species capable of metal reduction were also found, including Geobacter, Anaerolinea, and Longilinea spp. (relative combined abundances of 11% and 15% in phases 5 and 6, respectively).