The nitrate-ammonifying and nosZ-carrying bacterium Bacillus vireti is a potent source and sink for nitric and nitrous oxide under high nitrate conditions

摘要

Several Gram-positive bacteria carry genes for anaerobic reduction of NO_3~- via NO_2~- to NH_4~+ or gaseous nitrogen compounds, but the processes are understudied for these organisms. Here, we present results from a whole-genome analysis of the soil bacterium Bacillus vireti and a phenotypic characterization of intermediate and end-products, formed under anoxic conditions in the presence of NO_3~-. Bacillus vireti has a versatile metabolism. It produces acetate, formate, succinate and lactate from fermentation and performs dissimilatory nitrate reduction via NO_2~- to ammonium (DNRA) using NrfA, while NirB may detoxify NO_2~- in the cytoplasm. Moreover, it produces NO from an unknown source and reduces it via N_2O to N_2 using two enzymes connected to denitrification: an unusual NO reductase, qCuANor encoded by cbaA, and a z-type N_2O reductase, encoded by nosZ. In batch cultures, B. vireti reduced all NO_3~- to NO_2~- before the NO_2~- was reduced further. The quantities of all products varied with the initial NO_3~- concentration. With 5 mM NO_3~-, 90% was reduced to NH_4~+ while with ≥ 20 mM NO_3~-, 50% was reduced to NO, N_2O and N_2. This organism is thus an aggressive NO_2~- accumulator and may act as a net source and sink of NO and N_2O.