Distinct microbial community performing dissimilatory nitrate reduction to ammonium (DNRA) in a high C/NO3 – reactor

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 – and15NO2 –), 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. © 2018, Japanese Society of Microbial Ecology. All rights reserved.