Influence of nitrate and nitrite concentration on N2O production via dissimilatory nitrate/nitrite reduction to ammonium in Bacillus paralicheniformis LMG 6934

Abstract

Until now, the exact mechanisms for N2O production in dissimilatory nitrate/nitrite reduction to ammonium (DNRA) remain underexplored. Previously, we investigated this mechanism in Bacillus licheniformis and Bacillus paralicheniformis, ubiquitous gram-positive bacteria with many industrial applications, and observed significant strain dependency and media dependency in N2O production which was thought to correlate with high residual NO2−. Here, we further studied the influence of several physicochemical factors on NO3− (or NO2−) partitioning and N2O production in DNRA to shed light on the possible mechanisms of N2O production. The effects of NO3− concentrations under variable or fixed C/N-NO3− ratios, NO2− concentrations under variable or fixed C/N-NO2− ratios, and NH4+ concentrations under fixed C/N-NO3− ratios were tested during anaerobic incubation of soil bacterium B. paralicheniformis LMG 6934 (previously known as B. licheniformis), a strain with a high nitrite reduction capacity. Monitoring of growth, NO3−, NO2−, NH4+ concentration, and N2O production in physiological tests revealed that NO3− as well as NO2− concentration showed a linear correlation with N2O production. Increased NO3− concentration under fixed C/N-NO3− ratios, NO2− concentration, and NH4+ concentration had a significant positive effect on NO3− (or NO2−) partitioning ([N–NH4+]/[N–N2O]) toward N2O, which may be a consequence of the (transient) accumulation and subsequent detoxification of NO2−. These findings extend the information on several physiological parameters affecting DNRA and provide a basis for further study on N2O production during this process.