Burkholderia gladioli BNM349 as a promising source of bacterial metabolites for biocontrol of common bacterial blight of bean

Bacteria belonging to the Burkholderia genus have been extensively studied for their potential as biocontrol agents, particularly their ability to produce bioactive compounds. In this study, we investigated the antagonistic capabilities of an indigenous strain of Burkholderia gladioli BNM349 against a wide spectrum of bacterial and fungal phytopathogens. Culture filtrates and ethyl acetate extracts obtained from a stationary culture of BNM349 displayed antagonistic activity against gram-positive and gram-negative bacteria. Application of the organic extract on common bean (Phaseolus vulgaris L.) leaves significantly reduced the severity of common bacterial blight symptoms caused by Xanthomonas citri pv. fuscans. LC-MS/MS analysis detected several small molecules in the ethyl acetate extracts, including the azapteridine toxoflavin, cyclic lipopeptides icosalide A and B, and the macrolide antibiotic gladiolin and its isomers. Bioactivity assays also revealed that the bacterium inhibited fungal growth under co-culture conditions through antibiosis and mycophagous behavior. Moreover, whole genome sequencing of BNM349 revealed the presence of 29 biosynthetic gene clusters (BGCs). Notably, an uncharacterized BGC encoding a non-ribosomal peptide synthetase/polyketide synthase hybrid enzyme exhibited high similarity to the enzymes responsible for the synthesis of ralsolamycin, a lipopeptide previously identified in Ralstonia solanacearum and associated with its endofungal lifestyle. Another novel BGC was predicted to encode a prophage tail-like protein, which is also believed to be involved in the mycophagous ability demonstrated by BNM349. All these findings hold promise for future research, potentially revealing molecular mechanisms in BNM349 that can be exploited for sustainable plant disease management.