Abstract
Until now, the exact mechanisms for N(2) O 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 N(2) O production which was thought to correlate with high residual NO(2)(-) . Here, we further studied the influence of several physicochemical factors on NO(3)(-) (or NO(2)(-) ) partitioning and N(2) O production in DNRA to shed light on the possible mechanisms of N(2) O production. The effects of NO(3)(-) concentrations under variable or fixed C/N-NO(3)(-) ratios, NO(2)(-) concentrations under variable or fixed C/N-NO(2)(-) ratios, and NH(4)(+) concentrations under fixed C/N-NO(3)(-) 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, NO(3)(-) , NO(2)(-) , NH(4)(+) concentration, and N(2) O production in physiological tests revealed that NO(3)(-) as well as NO(2)(-) concentration showed a linear correlation with N(2) O production. Increased NO(3)(-) concentration under fixed C/N-NO(3)(-) ratios, NO(2)(-) concentration, and NH(4)(+) concentration had a significant positive effect on NO(3)(-) (or NO(2)(-) ) partitioning ([N-NH(4)(+) ]/[N-N(2) O]) toward N(2) O, which may be a consequence of the (transient) accumulation and subsequent detoxification of NO(2)(-) . These findings extend the information on several physiological parameters affecting DNRA and provide a basis for further study on N(2) O production during this process.