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Avermectins produced byStreptomyces avermitilis are commercially important anthelmintic agents. The detailed regulatory mechanisms of avermectin biosynthesis remain unclear. Here, we identified SAV3619, a TetR-family transcriptional regulator designated AveT, to be an activator for both avermectin production and morphological differentiation inS. avermitilis . AveT was shown to indirectly stimulate avermectin production by affecting transcription of the cluster-situated activator geneaveR . AveT directly repressed transcription of its own gene (aveT ), adjacent genepepD2 (sav_3620 ),sav_7490 (designatedaveM ), andsav_7491 by binding to an 18-bp perfect palindromic sequence (CGAAACG KTKYCGTTTCG , where K is T or G and Y is T or C and where the underlining indicates inverted repeats) within their promoter regions.aveM (which encodes a putative transmembrane efflux protein belonging to the major facilitator superfamily [MFS]), the important target gene of AveT, had a striking negative effect on avermectin production and morphological differentiation. Overexpression ofaveT and deletion ofaveM in wild-type and industrial strains ofS. avermitilis led to clear increases in the levels of avermectin production.In vitro gel-shift assays suggested that C-5–O-B1, the late pathway precursor of avermectin B1, acts as an AveT ligand. Taken together, our findings indicate positive-feedback regulation ofaveT expression and avermectin production by a late pathway intermediate and provide the basis for an efficient strategy to increase avermectin production inS. avermitilis by manipulation of AveT and its target gene product, AveM.

applied and environmental microbiology

Increasing Avermectin Production in Streptomyces avermitilis by Manipulating the Expression of a Novel TetR-Family Regulator and Its Target Gene Product