Distinct Microbial Community Performing Dissimilatory Nitrate Reduction to Ammonium (DNRA) in a High C/NO(3)(−) Reactor

A dissimilatory nitrate reduction to ammonium (DNRA) microbial community was developed under a high organic carbon to nitrate (C/NO(3)(−)) ratio in an anoxic semi-continuous sequencing batch reactor (SBR) fed with glucose as the source of carbon and NO(3)(−) as the electron acceptor. Activated sludge collected from a municipal wastewater treatment plant with good denitrification efficiency was used as the inoculum to start the system. The aim of this study was to examine the microbial populations in a high C/NO(3)(−) ecosystem for potential DNRA microorganisms, which are the microbial group with the ability to reduce NO(3)(−) to ammonium (NH(4)(+)). A low C/NO(3)(−) reactor was operated in parallel for direct comparisons of the microbial communities that developed under different C/NO(3)(−) values. The occurrence of DNRA in the high C/NO(3)(−) SBR was evidenced by stable isotope-labeled nitrate and nitrite ((15)NO(3)(−) and (15)NO(2)(−)), which proved the formation of NH(4)(+) from dissimilatory NO(3)(−)/NO(2)(−) reduction, in which both nitrogen oxides induced DNRA activity in a similar manner. An analysis of sludge samples with Illumina MiSeq 16S rRNA sequencing showed that the predominant microorganisms in the high C/NO(3)(−) SBR were related to Sulfurospirillum and the family Lachnospiraceae, which were barely present in the low C/NO(3)(−) system. A comparison of the populations and activities of the two reactors indicated that these major taxa play important roles as DNRA microorganisms under the high C/NO(3)(−) condition. Additionally, a beta-diversity analysis revealed distinct microbial compositions between the low and high C/NO(3)(−) SBRs, which reflected the activities observed in the two systems.