Regulation of nitrogen metabolism in the nitrate‐ammonifying soil bacterium B acillus vireti and evidence for its ability to grow using N 2 O as electron acceptor

Abstract

Summary B acillus vireti is a nitrate‐ammonifying bacterium and a partial denitrifier, reducing NO 3 − , NO 2 − , NO and N 2 O with NarG , NrfA , CbaA and NosZ respectively. Growth is optimized through successive use of the electron acceptors O 2 and NO 3 − , followed by NO 2 − , NO and N 2 O . Fermentation takes place simultaneously with anaerobic respiration. When grown in batch culture with 5 mM initial NO 3 − , transcription of nrfA was high and most NO 3 − was reduced to NH 4 + . With 20 mM initial NO 3 − , nrfA transcription was lower and more than 50% of the nitrate was recovered as NO , N 2 O and N 2 . Analysis of gene transcription patterns and corresponding gas kinetics indicated that O 2 and NO 2 − or NO are main controllers of nrfA , nirB , cbaA and nosZ transcription. This was corroborated by analyses of putative binding regions for specific transcriptional regulators. Furthermore, we demonstrate that N 2 O reduction in B . vireti supports growth. The high nosZ transcription but low N 2 O production seen at 5 mM NO 3 − implies that this organism can use N 2 O reductase to scavenge N 2 O from other organisms in the soil, thus possibly acting as a net sink for N 2 O .

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