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Regulation of Denitrification Genes in Neisseria meningitidis by Nitric Oxide and the Repressor NsrR

Jonathan D. Rock,^1, Melanie J. Thomson,^1, Robert C. Read,² and James W. B. Moir^1*

Department of Biology, University of York, Heslington, York YO10 5YW, United Kingdom,¹ School of Medicine and Biomedical Science, University of Sheffield, Beech Hill Road, Sheffield S10 2RX, United Kingdom²

Received 29 August 2006/ Accepted 13 November 2006

The human pathogen Neisseria meningitidis is capable of growth using the denitrification of nitrite to nitrous oxide under microaerobic conditions. This process is catalyzed by two reductases: nitrite reductase (encoded by aniA) and nitric oxide (NO) reductase (encoded by norB). Here, we show that in N. meningitidis MC58 norB is regulated by nitric oxide via the product of gene NMB0437 which encodes NsrR. NsrR is a repressor in the absence of NO, but norB expression is derepressed by NO in an NsrR-dependent manner. nsrR-deficient mutants grow by denitrification more rapidly than wild-type N. meningitidis, and this is coincident with the upregulation of both NO reductase and nitrite reductase even under aerobic conditions in the absence of nitrite or NO. The NsrR-dependent repression of aniA (unlike that of norB) is not lifted in the presence of NO. The role of NsrR in the control of expression of aniA is linked to the function of the anaerobic activator protein FNR: analysis of nsrR and fnr single and nsrR fnr double mutants carrying an aniA promoter lacZ fusion indicates that the role of NsrR is to prevent FNR-dependent aniA expression under aerobic conditions, indicating that FNR in N. meningitidis retains considerable activity aerobically.

Published ahead of print on 22 November 2006.

J.D.R. and M.J.T. contributed equally to this work.

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