Soil bacterium manipulates antifungal weapons by sensing intracellular type IVA secretion system effectors of a competitor.

Soil beneficial bacteria can effectively inhibit bacterial pathogens by assembling contact-dependent killing weapons, such as the type IVA secretion system (T4ASS). It's not clear whether these antibacterial weapons are involved in biotrophic microbial interactions in soil. Here we showed that an antifungal antibiotic 2,4-DAPG production of the soil bacterium, Pseudomonas protegens can be triggered by another soil bacterium, Lysobacter enzymogenes, via T4ASS by co-culturing on agar plates to mimic cell-to-cell contact. We demonstrated that the induced 2,4-DAPG production of P. protegens is achieved by intracellular detection of the T4ASS effector protein Le1519 translocated from L. enzymogenes. We defined Le1519 as LtaE (Lysobacter T4E triggering antifungal effects), which specifically stimulates the expression of 2,4-DAPG biosynthesis genes in P. protegens, thereby protecting soybean seedlings from infection by the fungus Rhizoctonia solani. We further found that LtaE directly bound to PhlF, a pathway-specific transcriptional repressor of the 2,4-DAPG biosynthesis, then activated the 2,4-DAPG production. Our results highlight a novel pattern of microbial interspecies and interkingdom interactions, providing a unique case for expanding the diversity of soil microbial interactions.