Molecular adaptations and metabolic reprogramming of Priestia megaterium KW16 in response to fungal pathogen-derived filtrates

Abstract Priestia megaterium KW16 is an endophytic bacterium with broad-spectrum antifungal activity, but its molecular response to phytopathogens remains unknown. Here, we combined transcriptomics, metabolomics, RT-qPCR, and fatty acid profiling to characterise the response of KW16 to cell-free culture filtrates of pathogenic fungi: Colletotrichum dematium , Fusarium avenaceum , Rhizoctonia solani , and Sclerotinia sclerotiorum . KW16 inhibited the growth of all tested fungi, with the strongest effect observed against S. sclerotiorum (> 50%), followed by C. dematium, R. solani, and F. avenaceum . Transcriptomic analysis identified 2440 unique differentially expressed genes, with S. sclerotiorum inducing the largest response (1149 upregulated and 1058 downregulated genes). A conserved response across all treatments included repression of sporulation-associated genes and induction of genes involved in iron acquisition, acetate utilisation, stress adaptation, and cell wall remodelling. Our results demonstrated that exposure to fungal filtrates upregulated the genes encoding gas vesicle biosynthesis, competence-associated functions, and lasso peptide biosynthetic genes, particularly in response to S. sclerotiorum . The fungal-derived metabolites could serve as both nutritional resources and ecological signals, driving extensive physiological reprogramming in KW16 and revealing molecular mechanisms that may underlie its persistence and biocontrol activity in competitive plant-associated environments.