A genetically safe Burkholderia cenocepacia strain P3 suppresses Cercospora zeina via siderophore-mediated iron deprivation

Abstract

Gray leaf spot (GLS), caused by Cercospora zeina, is a devastating fungal disease of maize worldwide. This study reports the isolation of a novel rhizobacterium, strain P3, from the maize rhizosphere, which was identified as Burkholderia cenocepacia based on phylogenetic analysis of 16S rRNA and dnaG genes. Strain P3 exhibited broad-spectrum antifungal activity against multiple pathogens and demonstrated plant growth-promoting traits. Genomic analysis confirmed the absence of major virulence genes, supporting its environmental safety. Fermentation conditions for siderophore production were optimized, achieving a yield of 85.5 % siderophore units under optimal conditions (sucrose 5 g/L, asparagine 3 g/L, pH 7.0, 32 °C). The fermentation supernatant of P3 inhibited C. zeina growth dose-dependently, causing hyphal membrane damage and reactive oxygen species accumulation. Two siderophores, pyochelin and ornibactin, were identified and shown to synergistically suppress fungal growth under iron-limited conditions. Greenhouse trials demonstrated that pretreatment with strain P3 significantly reduced lesion area and disease severity in maize plants challenged with C. zeina. These results indicate that B. cenocepacia P3 is a promising, environmentally friendly biocontrol agent with strong potential for integrated management of gray leaf spot.