Novel mechanism of hydrogen peroxide for promoting efficient natamycin synthesis in Streptomyces .

The mechanism of regulation of natamycin biosynthesis by Streptomyces in response to oxidative stress is unclear. Here, we first show cholesterol oxidase SgnE, which catalyzes the formation of H 2 O 2 from sterols, triggered a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus . In response to reactive oxygen species, residues Cys212 and Cys221 of the H 2 O 2 -sensing consensus sequence of OxyR were oxidized, resulting in conformational changes in the protein: OxyR extended its DNA-binding domain to interact with four motifs of promoter p sgnM . This acted as a redox-dependent switch to turn on/off gene transcription of sgnM , which encodes a cluster-situated regulator, by controlling the affinity between OxyR and p sgnM , thus regulating the expression of 12 genes in the natamycin biosynthesis gene cluster. OxyR cooperates with SgnR, another cluster-situated regulator and an upstream regulatory factor of SgnM, synergistically modulated natamycin biosynthesis by masking/unmasking the -35 region of p sgnM depending on the redox state of OxyR in response to the intracellular H 2 O 2 concentration. IMPORTANCE Cholesterol oxidase SgnE is an indispensable factor, with an unclear mechanism, for natamycin biosynthesis in Streptomyces . Oxidative stress has been attributed to the natamycin biosynthesis. Here, we show that SgnE catalyzes the formation of H 2 O 2 from sterols and triggers a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus . OxyR, which cooperates with SgnR, acted as a redox-dependent switch to turn on/off gene transcription of sgnM , which encodes a cluster-situated regulator, by masking/unmasking its -35 region, to control the natamycin biosynthesis gene cluster. This work provides a novel perspective on the crosstalk between intracellular ROS homeostasis and natamycin biosynthesis. Application of these findings will improve antibiotic yields via control of the intracellular redox pressure in Streptomyces .