Nitric oxide is not only an obligatory intermediate in denitrification, but also a signalling and defence molecule of major importance. However, the basis of resistance to NO and RNS (reactive nitrogen species) is poorly understood in many microbes. The cellular targets of NO and RNS [e.g. metalloproteins, thiols in proteins, glutathione and Hcy (homocysteine)] may themselves serve as signal transducers, sensing NO and RNS, and resulting in altered gene expression and synthesis of protective enzymes. The properties of a number of such protective mechanisms are outlined here, including globins, flavorubredoxin, diverse enzymes with NO- or S-nitrosothiol-reducing properties and other redox proteins with poorly defined roles in protection from nitrosative stresses. However, the most fully understood mechanism for NO detoxification involves the enterobacterial flavohaemoglobin (Hmp). Aerobically, Hmp detoxifies NO by acting as an NO denitrosylase or ‘oxygenase’ and thus affords inducible protection of growth and respiration, and aids survival in macrophages. The flavohaemoglobin-encoding gene of Escherichia coli, hmp, responds to the presence of NO and RNS in an SoxRS-independent manner. Nitrosating agents, such as S-nitrosoglutathione, deplete cellular Hcy and consequently modulate activity of the MetR regulator that binds the hmp promoter. Regulation of Hmp synthesis under anoxic conditions involves nitrosylation of 4Fe-4S clusters in the global transcriptional regulator, FNR. The foodborne microaerophilic pathogen, Campylobacter jejuni, also expresses a haemoglobin, Cgb, but it does not possess the reductase domain of Hmp. A Cgb-deficient mutant of C. jejuni is hypersensitive to RNS, whereas cgb expression and holoprotein synthesis are specifically increased on exposure to RNS, resulting in NO-insensitive respiration. A ‘systems biology’ approach, integrating the methodologies of bacterial molecular genetics and physiology with post-genomic technologies, promises considerable advances in our understanding of bacterial NO tolerance mechanisms in pathogenesis.
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Conference Article|
February 01 2005
Nitric oxide and nitrosative stress tolerance in bacteria
R.K. Poole
R.K. Poole
1
1Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, U.K.
1email r.poole@sheffield.ac.uk
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Publisher: Portland Press Ltd
Received:
September 24 2004
Online ISSN: 1470-8752
Print ISSN: 0300-5127
© 2005 The Biochemical Society
2005
Biochem Soc Trans (2005) 33 (1): 176–180.
Article history
Received:
September 24 2004
Citation
R.K. Poole; Nitric oxide and nitrosative stress tolerance in bacteria. Biochem Soc Trans 1 February 2005; 33 (1): 176–180. doi: https://doi.org/10.1042/BST0330176
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