Borrelidin-producing and root-colonizing Streptomyces rochei is a potent biopesticide for two soil-borne oomycete-caused plant diseases

Abstract

Biopesticides are an attractive biotechnological alternative to conventional pesticides for soil-borne plant diseases. A screening strategy with over 100 actinomycetes bacteria isolated from diverse rhizosphere soils uncovered the Streptomyces rochei strain JK1 as a potent inhibitor of oomycete growth. The culture filtrates of the JK1 strain inhibited oomycete growth in plate assays and could suppress two major oomycete-caused plant diseases caused by Pythium myriotylum and Phytophthora sojae. The macrolide secondary metabolite borrelidin was identified using HR-ESI-MS and NMR from growth-inhibitory fractions and inhibited both oomycete growth and plant diseases. The biosynthetic gene clusters in the genome of S. rochei JK1 show the potential to produce other secondary metabolites as well as borrelidin. The JK1 biosynthetic gene clusters are partly conserved among the publicly available S. rochei genomes, whereby each JK1 cluster was shared with at least one of eight other S. rochei strains. The S. rochei JK1 strain, which was isolated from the rhizosphere of soybean plants, colonized soybean roots as well as ginger roots suggesting competence in diverse rhizospheres. The biotechnological application of the strain and fermentation products is emphasized by how the oomycete growth inhibition of the culture filtrate was stable across a range of temperature and pH levels. The genomic, and metabolite data, mechanistic-insights into disease control, and the range of oomycete-caused diseases controlled, all support the S. rochei JK1 strain as an important new bioresource.