Distinct Microbial Community Performing Dissimilatory Nitrate Reduction to Ammonium (DNRA) in a High C/NO3- Reactor.

A dissimilatory nitrate reduction to ammonium (DNRA) microbial community was developed under a high organic carbon to nitrate (C/NO3-) ratio in an anoxic semi-continuous sequencing batch reactor (SBR) fed with glucose as the source of carbon and NO3- 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/NO3- ecosystem for potential DNRA microorganisms, which are the microbial group with the ability to reduce NO3- to ammonium (NH4+). A low C/NO3- reactor was operated in parallel for direct comparisons of the microbial communities that developed under different C/NO3- values. The occurrence of DNRA in the high C/NO3- SBR was evidenced by stable isotope-labeled nitrate and nitrite (15NO3- and 15NO2-), which proved the formation of NH4+ from dissimilatory NO3-/NO2- 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/NO3- SBR were related to Sulfurospirillum and the family Lachnospiraceae, which were barely present in the low C/NO3- 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/NO3- condition. Additionally, a beta-diversity analysis revealed distinct microbial compositions between the low and high C/NO3- SBRs, which reflected the activities observed in the two systems.