title: Transcriptional and metabolic regulation of denitrification in Paracoccus denitrificans allows low but significant activity of nitrous oxide reductase under oxic conditions.
abstract: Oxygen is known to repress denitrification at the transcriptional and metabolic levels. It has been a common notion that nitrous oxide reductase (N2 OR) is the most sensitive enzyme among the four N-oxide reductases involved in denitrification, potentially leading to increased N2 O production under suboxic or fluctuating oxygen conditions. We present detailed gas kinetics and transcription patterns from batch culture experiments with Paracoccus denitrificans, allowing in vivo estimation of e(-) -flow to O2 and N2 O under various O2 regimes. Transcription of nosZ took place concomitantly with that of narG under suboxic conditions, whereas transcription of nirS and norB was inhibited until O2 levels approached 0 μM in the liquid. Catalytically functional N2 OR was synthesized and active in aerobically raised cells transferred to vials with 7 vol% O2 in headspace, but N2 O reduction rates were 10 times higher when anaerobic pre-cultures were subjected to the same conditions. Upon oxygen exposure, there was an incomplete and transient inactivation of N2 OR that could be ascribed to its lower ability to compete for electrons compared with terminal oxidases. The demonstrated reduction of N2 O at high O2 partial pressure and low N2 O concentrations by a bacterium not known as a typical aerobic denitrifier may provide one clue to the understanding of why some soils appear to act as sinks rather than sources for atmospheric N2 O.
authors.affiliation: Department of Environmental Sciences, Norwegian University of Life Sciences, PO Box 5003, N-1432, Ås, Norway.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Qu
authors.affiliation: Department of Environmental Sciences, Norwegian University of Life Sciences, PO Box 5003, N-1432, Ås, Norway.
authors.forename: Lars R
authors.initials: LR
authors.lastname: Bakken
authors.affiliation: Department of Environmental Sciences, Norwegian University of Life Sciences, PO Box 5003, N-1432, Ås, Norway.
authors.forename: Lars
authors.initials: L
authors.lastname: Molstad
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, N-1432, Ås, Norway.
authors.forename: Åsa
authors.initials: Å
authors.lastname: Frostegård
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, PO Box 5003, N-1432, Ås, Norway. linda.bergaust@nmbu.no.
authors.forename: Linda L
authors.initials: LL
authors.lastname: Bergaust
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058440:Denitrification; D015964:Gene Expression Regulation, Bacterial; D009609:Nitrous Oxide / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010231:Paracoccus denitrificans / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D012987:Soil / Q000737:chemistry; D012988:Soil Microbiology; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D012987:Soil; D010088:Oxidoreductases; C022763:nitrous oxide reductase; D009609:Nitrous Oxide; D010100:Oxygen