ECF-σ5 in Sreptomyces avermitilis is involved in regulation of avermectin biosynthesis and stress response

Abstract:

[Objective] We investegated the role of extracytoplasmic function (ECF) σ factor, σ⁵, in avermectin biosynthesis, morphological differentiation and stress response in S. avermitilis. [Methods] We constructed sig5 gene deletion, complementation and overexpression strains and determined the role of σ⁵ in avermectin production and morphological differentiation by shaking flask fermentation and morphological observation of these strains. We used RT-qPCR, EMSA and ChIP assays to identify the target genes of σ⁵. We used stress tests to reveal the stress response that σ⁵ may be involved in. [Results] Determination of avermectin production and morphological observation in sig5 related strains implied that σ⁵ inhibits avermectin production, but has no effect on growth or morphology. Deletion of sig5 increased transcription levels of pathway-specific activator gene aveR and structural gene aveA1, but σ⁵ did not bind to the promoter regions of aveR and aveA1. RT-qPCR and ChIP assays showed that σ⁵ positively regulates the transcription of itself and adjacent genes by binding to the promoter regions of sig5, SAV612, SAV615 and SAV618. Stress tests suggested that σ⁵ is involved in responding to osmotic stress. [Conclusion] Our findings indicated that σ⁵ indirectly inhibits avermectin production by affecting transcription of ave genes.

Key words:Streptomyces avermitilis;avermectin;ECF-σ factor;σ⁵