A draft genome sequence of Streptomyces ansochromogenes 7100 was generated using 454 sequencing technology. In combination with local BLAST searches and gap filling techniques, a comprehensive antiSMASH-based method was adopted to assemble the secondary metabolite biosynthetic gene clusters in the draft genome of S. ansochromogenes. A total of at least 35 putative gene clusters were identified and assembled. Transcriptional analysis showed that 20 of the 35 gene clusters were expressed in either or all of the three different media tested, whereas the other 15 gene clusters were silent in all three different media. This study provides a comprehensive method to identify and assemble secondary metabolite biosynthetic gene clusters in draft genomes of Streptomyces, and will significantly promote functional studies of these secondary metabolite biosynthetic gene clusters.
Secondary metabolites are organic compounds with complex chemical structures and diverse physiological functions. Secondary metabolites include antibiotics, pigments, and other bioactive compounds. Many of these compounds have important agricultural and medical applications. Microorganisms, especially actinomycetes and filamentous fungi, are noted as a rich source of bioactive secondary metabolites. Typically, each species produces several antibiotics, with the profile being species-specific.
The biosynthesis of antibiotics is controlled by cascade regulation involving cluster-situated regulators (CSRs) and pleiotropic regulators. Three CSRs have been identified in the jadomycin biosynthetic gene cluster, including one OmpR-type activator (JadR1) and two TetR-like repressors (JadR* and JadR2). To examine their interactions in jadomycin biosynthesis, a series of mutants were generated and tested for jadomycin production. We noticed that jadomycin production in the jadR*-jadR2 double mutant was increased dramatically compared with either single mutant. Transcriptional analysis showed that jadR* and jadR2 act synergistically to repress jadomycin production by inhibiting the transcription of jadR1. Furthermore, jadR* and jadR2 reciprocally inhibit each other. The complex interactions among these three CSRs may provide clues for the activation of the jadomycin gene cluster, which would otherwise remain silent without stimulation from stress signals.
