Fig. 5

Proposed model of intracellular nitric oxide (NO) homeostasis in Streptomyces coelicolor A3(2) M145. Flavohaemoglobin (Fhb) and nitrate reductase (Nar) mediate the circulation of NO, NO₃⁻, and NO₂.⁻. DevS/R is activated or inactivated depending on intracellular NO levels. NO directly regulates actinorhodin synthesis through the DevS/R two-component regulatory system, which modulates actII-ORF4 expression. DevR also regulates nar2 expression and NO production. Intracellular NO homeostasis is maintained through Fhb metabolism and its interaction with mycothiol (MSH) (S-nitrosylation) to form S-nitrosomycothiol (MSNO)