Abstract
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.
