EFFECTS OF DIFFERENT DISSOLVED OXYGEN CONDITIONS ON AEROBIC DENITRIFYING BACTERIA IN A COMPLEX MICROBIAL COMMUNITY

Abstract

 The effect of dissolved oxygen (DO) concentration on aerobic denitrification activity and denitrifying bacterial communities was investigated. Since the conventional shaking culture method cannot control constant DO concentration, in this study, we constructed an apparatus to maintain constant DO concentration by controlling aeration and conducted aerobic denitrification tests under low DO (3 ± 1 mg/L), medium DO (5 ± 1 mg/L), and high DO (7 ± 2 mg/L) conditions. Under all aerobic conditions, NO₃^-_-N concentrations decreased simultaneously with NH₄⁺_-N and COD_Cr, and aerobic denitrification reaction proceeded simultaneously with nitrification reaction. Prokaryotic community structure analysis based on 16S rRNA genes did not confirm the presence of independent aerobic ammonia-oxidizing bacteria/archaea, suggesting that the ammonia oxidation reaction was carried out by aerobic denitrifying bacteria (heterotrophic bacteria). The microbial community structure was simpler under high DO conditions, with Paracoccus spp. and Pseudomonas spp. dominating under high and low DO conditions, respectively.