A critical role for staphylococcal nitric oxide synthase in controlling flavohemoglobin toxicity

Ryan M. Singh, Sujata S. Chaudhari, Sasmita Panda, Elizabeth H. Hutfless, Cortney E. Heim, Dhananjay Shinde, Abdulelah A. Alqarzaee, Margaret Sladek, Vineet Kumar, Matthew C. Zimmerman, Paul D. Fey, Tammy Kielian, Vinai C. Thomas

Research output: Contribution to journalArticlepeer-review


Most coagulase-negative staphylococcal species, including the opportunistic pathogen Staphylococcus epidermidis, struggle to maintain redox homeostasis and grow under nitrosative stress. Under these conditions, growth can only resume once nitric oxide (NO) is detoxified by the flavohemoglobin Hmp. Paradoxically, S. epidermidis produces endogenous NO through its genetically encoded nitric oxide synthase (seNOS) and heavily relies on its activity for growth. In this study, we investigate the basis of the growth advantage attributed to seNOS activity. Our findings reveal that seNOS supports growth by countering Hmp toxicity. S. epidermidis relies on Hmp activity for its survival in the host under NO stress. However, in the absence of nitrosative stress, Hmp generates significant amounts of the harmful superoxide radical (O2•-) from its heme prosthetic group which impedes growth. To limit Hmp toxicity, nitrite (NO2) derived from seNOS promotes CymR-CysK regulatory complex activity, which typically regulates cysteine metabolism, but we now demonstrate to also repress hmp transcription. These findings reveal a critical mechanism through which the bacterial NOS-Hmp axis drives staphylococcal fitness.

Original languageEnglish (US)
Article number102935
JournalRedox Biology
StatePublished - Nov 2023


  • Bacterial nitric oxide synthase
  • Flavohemoglobin
  • Respiration
  • Staphylococcus epidermidis
  • Superoxide

ASJC Scopus subject areas

  • Organic Chemistry


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