Studies On The Mechanism Underlying The Negative Regulation Of Antibiotic Production By Over-Expressed TetR Regulator SCO3201 In Streptomyces Coelicolor

Streptomyces is known as prolific producers of active secondary metabolites such as antibiotics.According to statistics,more than 70%of clinically used antibiotics and various biologically active compounds used in agriculture and food industry are produced from Streptomyces.Therefore,in-depth study of the mechanism governing the secondary metabolism of Streptomyces is of great significance to many fields including medicine,health,industry and agriculture.At present,genomes of up to dozens of Streptomyces strains?most of which are model strains?have been published.The availability of these information greatly facilitate the deeper research on the secondary metabolism of Streptomyces at the molecular level,thus promoting the discovery and activation of the cryptic clusters driving the synthesis of unknown secondary metabolites.It has been previously demonstrated that,the over-expressed SCO3201,a regulator of the TetR family,strongly inhibit antibiotic production and morphological differentiation in Streptomyces coelicolor M145.In order to elucidate the molecular processes underlying this interesting,but poorly understood phenomenon,a comparative analysis of the transcriptomes of the strain over-expressing sco3201 and of the control strain containing the empty plasmid was carried out.This study revealed that genes encoding proteins involved in lipid metabolism as well as,in some instances,TetR regulators adjacent to them were differentially expressed in the two strains.Overall,the expression of most genes involved in fatty acid biosynthesis?FAB?was up-regulated?including sco2387,sco0117,sco3246,sco6564,sco3248 and other genes?whereas that of genes involved in fatty acid degradation?FAD?was down-regulated?including sco4502,sco6475,sco6787,sco6789,sco6790 and other genes?in sco3201 over-expressed strain.Consistently the lipid content of this strain was 2.5 fold higher than that of control strain indicating the direct or indirect control of the expression of these genes by SCO3201.The direct interaction of purified His₆-SCO3201 with the promoter regions of 4TetR regulators?sco0116,sco0430,sco4167 and sco6792?that likely regulate positively or negatively the expression of their neighboring genes involved in lipid metabolism and with that of Fas R/SCO2386,the activator of the expression of the main fatty acid biosynthetic operon sco2386-sco2390,was demonstrated.The high lipid content resulting from sco3201 over-expression is predicted to lead to a drastic reduction of acetyl Co A availability that impaired antibiotic biosynthesis either directly or indirectly.The results presented here indicates that the inhibition of antibiotic production in Streptomyces coelicolor over-expressing the TetR regulator SCO3201 is correlated with an enhanced lipid content,and provides guidance and practical basis for the activation of cryptic clusters as well as the further discovery of novel antibiotics.