Insight into functionally active bacteria in nitrification following Na+ and Mg2+ exposure based on 16S rDNA and 16S rRNA sequencing

Abstract

Despite increasing interests in osmotic membrane bioreactors, the information regarding the bacterial toxicity effects of reversely transported draw solute (RTDS) is limited. In this study, two representative draw solutes (NaCl and MgCl2) were used at different concentrations (0, 2.5, 5.0, 7.5 and 10.0 g/L) to evaluate their toxicity in a continuous nitrifying bioreactor. Notably, Mg2+ selectively inhibited the activity of ammonia-oxidizing bacteria (AOB), which decreased to 11.3% at 7.5 g-Mg2+/L. The rRNA-based analysis was more effective than the rDNA-based analysis to elucidate the relationship between active communities of nitrifying bacteria and the actual nitrifying performance. Nitrosomonas europaea, a representative AOB, was vulnerable to Mg2+ in comparison to Na+. In contrast, the dominant nitrite-oxidizing bacteria (NOB), Nitrobacter winogradskyi and Nitrolancea hollandica, maintained a relevant level of relative abundance for achieving nitrite oxidation after exposure to 10 g/L Na+ and Mg2+. This fundamental inhibition information of the draw solute can be applied to set the operational regime preventing the critical solute concentration in mixed liquor of nitrifying OMBRs.