Two master switch regulators trigger A40926 biosynthesis in Nonomuraea sp. strain ATCC 39727

The actinomycete Nonomuraea sp. ATCC 39727 produces the glycopeptide A40926, the precursor of dalbavancin. Biosynthesis of A40926 is encoded by the dbv gene cluster which contains 37 protein coding sequences that participate in antibiotic biosynthesis, regulation, immunity, and export. In addition to the positive regulatory protein Dbv4, the A40926 biosynthetic gene cluster encodes two additional putative regulators, Dbv3 and Dbv6. Independent mutations in these genes, combined with bioassays and LC-MS analyses, demonstrated that Dbv3 and Dbv4 are both required for antibiotic production, while inactivation of dbv6 had no effect. In addition, over-expression of dbv3 led to higher levels of A40926 production. Transcriptional and quantitative RT-PCR analyses showed that Dbv4 is essential for the transcription of two operons, dbv14-dbv8 and dbv30-dbv35, while Dbv3 positively controls the expression of four monocistronic transcription units (dbv4, dbv29, dbv36, dbv37) and of six operons (dbv2-dbv1, dbv14-dbv8, dbv17-dbv15, dbv21-dbv20, dbv24-dbv28, dbv30-dbv35). We propose a complex and coordinated model of regulation in which Dbv3 directly or indirectly activates transcription of dbv4 and controls biosynthesis of 4-hydroxyphenylglycine and the heptapeptide backbone, A40926 export and some tailoring reactions (mannosylation and hexose oxidation), while Dbv4 regulates directly biosynthesis of 3,5-dihydroxyphenylglycine and other tailoring reactions including the four cross-links, halogenation, glycosylation and acylation.