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Appl. Environ. Microbiol. doi:10.1128/AEM.01533-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Nitric oxide reductase gene expression and nitrous oxide production in Pseudomonas mandelii grown with nitrate

Potato Research Centre, Agriculture and Agri-Food Canada, Fredericton, NB, Canada E3B 4Z7; Department of Environmental Biology, University of Guelph, Guelph, ON, Canada N1G 2W1; Nova Scotia Agricultural College, Department of Environmental Sciences, Truro, NS, Canada B2N 5E3

^* To whom correspondence should be addressed. Email: goyercm{at}agr.gc.ca. jtrevors{at}uoguelph.ca.

	Abstract

Pure cultures of P. mandelii were incubated with or without nitrate, which acts as a substrate and an electron acceptor for denitrification. Nitric oxide reductase (cnorB) gene expression was quantified using a quantitative reverse transcription quantitative PCR (qRT-PCR) and nitrous oxide emissions were measured by gas chromatography. P. mandelii cells in either the presence or absence of nitrate demonstrated an increase in cnorB gene expression during the first 3 h of growth. Gene expression of cnorB remained high (average 2.06 x 10⁸ transcripts/µg RNA) in nitrate amended cells while in untreated cells it decreased to an average of 3.63 x 10⁶ transcripts/µg RNA from 4 h to 6 h. Nitrous oxide accumulation in the headspace was detected at 2 h and cumulative emissions continued to increase over a 24-h period to 101 µmoles in nitrate amended cells. P. mandelii cnorB gene expression was not detected under aerobic conditions. These results demonstrate that P. mandelii cnorB gene expression was induced 203-fold at 4h when nitrate was present in the medium. Accumulations of N₂O indicated that the cNorB enzyme was synthesized and active.