Modulation of actinorhodin biosynthesis in Streptomyces lividans by glucose repression of afsR2 gene transcription

While the biosynthetic gene cluster encoding the pigmented antibiotic actin orhodin (ACT) is present in the two closely related bacterial species, Stre ptomyces lividans and Streptomyces coelicolor, it normally is expressed onl y in S. coelicolor-generating the deep-blue colonies responsible for the S, coelicolor name. However, multiple copies of the two regulatory genes, afs R and afsR2, activate ACT production in S. lividans, indicating that this s treptomycete encodes a functional ACT biosynthetic pathway. Here we report that the occurrence of ACT biosynthesis in S, lividans is determined condit ionally by the carbon source used for culture. We found that the growth of S, lividans on solid media containing glucose prevents ACT production in th is species by repressing the synthesis of afsR2 mRNA; a shift to glycerol a s the sole carbon source dramatically relieved this repression, leading to extensive ACT synthesis and obliterating this phenotypic distinction betwee n S, lividans and S, coelicolor, Transcription from the afsR2 promoter duri ng growth in glycerol was dependent on afsR gene function and was developme ntally regulated, occurring specifically at the time of aerial mycelium for mation and coinciding temporally with the onset of ACT production, In liqui d media, where morphological differentiation does not occur, ACT production in the absence of glucose increased as S, lividans cells entered stationar y phase, but unlike ACT biosynthesis on solid media, occurred by a mechanis m that did not require either afsR or afsR2, Our results identify parallel medium-dependent pathways that regulate ACT biosynthesis in S, lividans and further demonstrate that the production of this antibiotic in S, lividans grown on agar can be modulated by carbon source through the regulation of a fsR2 mRNA synthesis.