Identification and genomic analyses of a novel actinobacterium Streptomyces shaowuensis sp. nov. with biocontrol potential for rice bacterial blight

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is one of the most severe bacterial diseases in rice. The current BLB-prevention strategy depends on chemical antimicrobials. The biological control methods have gained considerable attention. Among them, Streptomyces are particularly promising candidates due to their ability to produce diverse natural antimicrobial and plant-growth-promoting metabolites. In this study, we isolated a Streptomyces strain HSW2009 from the rice rhizosphere. This strain displayed significant antagonistic activity against Xoo. The antagonistic metabolite was extracted and purified from the HSW2009 culture. High-performance liquid chromatography-mass chromatography and nuclear magnetic resonance analyses revealed that the active compound is Piericidin A1, a member of the piericidin family metabolites containing a 4-pyridinol core linked with a methylated polyketide side chain. Piericidin A1 was shown to protect rice from Xoo infection in the microclimate chamber. The strain HSW2009 produced pale yellow aerial mycelia on the agar plate of the International Streptomyces Project-2 medium. Its cellular morphology conformed to that typically observed in the genus Streptomyces. Phylogenetic analysis of 16S rRNA gene sequences showed that HSW2009 was closely related to Streptomyces zagrosensis, S. youssoufiensis, and S. varsoviensis. HSW2009 displayed a unique DNA profile in BOX-PCR fingerprinting analysis and had a genome size of 8,806,972 bp, with a 72.83% G + C content. Average nucleotide identity analysis and digital DNA–DNA hybridization using the Type Strain Genome Server supported HSW2009 as a novel Streptomyces sp. It was therefore proposed as Streptomyces shaowuensis sp. nov., type strain HSW2009.