Examination of the Staphylococcus aureus nitric oxide reductase (saNOR) reveals its contribution to modulating intracellular NO levels and cellular respiration

• Published in: Molecular microbiology 2015-05, Vol.96 (3), p.651-669
• Main Authors: Lewis, A. M., Matzdorf, S. S., Endres, J. L., Windham, I. H., Bayles, K. W., Rice, K. C.
• Format: Article
• Language: English
• Subjects: Biofilms; Gene Deletion; Gene expression; Genetic Complementation Test; Gram-positive bacteria; Nitric oxide; Nitric Oxide - metabolism; Nitric Oxide - toxicity; Oxidation-Reduction; Oxidoreductases - genetics; Oxidoreductases - metabolism; Respiration; Staphylococcus aureus - enzymology; Staphylococcus aureus - genetics; Staphylococcus aureus - growth & development; Staphylococcus aureus - metabolism; Stress, Physiological
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.12962

Staphylococcus aureus nitrosative stress resistance is due in part to flavohemoprotein (Hmp). Although hmp is present in all sequenced S. aureus genomes, 37% of analyzed strains also contain nor, encoding a predicted quinol‐type nitric oxide (NO) reductase (saNOR). DAF‐FM staining of NO‐challenged wild‐type, nor, hmp and nor hmp mutant biofilms suggested that Hmp may have a greater contribution to intracellular NO detoxification relative to saNOR. However, saNOR still had a significant impact on intracellular NO levels and complemented NO detoxification in a nor hmp mutant. When grown as NO‐challenged static (low‐oxygen) cultures, hmp and nor hmp mutants both experienced a delay in growth initiation, whereas the nor mutant's ability to initiate growth was comparable with the wild‐type strain. However, saNOR contributed to cell respiration in this assay once growth had resumed, as determined by membrane potential and respiratory activity assays. Expression of nor was upregulated during low‐oxygen growth and dependent on SrrAB, a two‐component system that regulates expression of respiration and nitrosative stress resistance genes. High‐level nor promoter activity was also detectable in a cell subpopulation near the biofilm substratum. These results suggest that saNOR contributes to NO‐dependent respiration during nitrosative stress, possibly conferring an advantage to nor+ strains in vivo. The nor gene, encoding a quinol‐type nitric oxide reductase (saNOR), was identified in a number of S. aureus genomes belonging to healthcare‐associated and livestock‐associated MRSA lineages. Expression of nor was upregulated during low‐oxygen growth, and high‐level promoter activity was observed in a cell subpopulation. A role for saNOR in NO detoxification and anaerobic respiration when grown in low‐oxygen NO‐challenged cultures was demonstrated, suggesting that saNOR may confer a survival advantage to S. aureus during infection.