Genome-wide screening antifungal genes in Streptomyces griseus S4-7, a Fusarium wilt disease suppressive microbial agent

Abstract

Streptomyces is a widely studied bacterial genus, particularly with regard to secondary metabolites and antibiotics production. Streptomyces griseus S4-7 was isolated from a strawberry Fusarium wilt disease suppressive soil, and its biological control ability has been well established. However, the antifungal mechanism of strain S4-7 is not yet fully understood at the molecular and biochemical level. Therefore, in this study we created a random mutant library for strain S4-7 with the Tn5 transposon element to investigate antifungal traits on a genome-wide scale. In total 4646 individual mutant strains were created and 13 mutants were selected based on loss of antifungal activity. The knockout genes were identified as electron transfer oxidoreductase (eto), sigma factor-70 (sig70) and nrps by Inverse PCR (I-PCR). eto regulates the geranylgeranyl reductase gene, which is involved in terpenoid-quinone biosynthesis, an important factor in cell fitness. In the Delta eto strain, expression of wbl, a master regulator of the production of secondary metabolites, was significantly reduced. sig70 is responsible for the cell differentiation sensing mechanism in genus Streptomyces. Delta nrps showed decreased production of hybrid peptide-polyketide siderophores. These results suggest that S. griseus S4-7may have various antifungal mechanisms, and each mechanism is essential to maximal antifungal activity.