Hijacking competitor-derived signals: RcsB/C drives Lysobacter enzymogenes to exploit farnesol for enhanced antifungal capacity.

Microbial antagonism is a fundamental ecological process that shapes community composition and maintains ecosystem balance. However, the molecular signals, such as cross-kingdom interactions between bacteria and fungi in natural environments, remain largely unexplored. Lysobacter enzymogenes is a widespread predatory bacterium that produces the antifungal secondary metabolite heat-stable antifungal factor (HSAF), which enables interactions with diverse fungi. Here, we investigated the interkingdom interactions between L. enzymogenes and the environmental fungus Candida krusei, both of which are widely distributed, to elucidate the bacterial-fungal communication. We found that the antagonistic effect of bacteria-fungi was significant under both contact and non-contact co-culture conditions, indicating the involvement of diffusible metabolites. Given that farnesol is a common quorum-sensing (QS) molecule in Candida, metabolite profiling combined with exogenous addition and biosynthesis inhibition experiments demonstrated that farnesol functions as a cross-kingdom signal regulating HSAF production and bacterial antagonism. Further mechanistic analysis of the intrinsic mechanism revealed that the two-component system (TCS) RcsB/C in L. enzymogenes can sense farnesol and activate the production of HSAF through the MarR family regulators, mediating the antagonistic pathway. In addition, our work identified the key amino acid residues in RcsC of L. enzymogenes responsible for recognizing farnesol. In summary, we report the bacterial TCS involved in farnesol sensing and reveal a novel bacterial-fungal antagonistic mechanism, in which L. enzymogenes "hijacks" a fungal QS molecule to enhance its antifungal capacity, uncovering a previously unrecognized strategy of cross-kingdom communication.IMPORTANCEBacteria and fungi frequently interact in shared habitats, yet the chemical cues that shape these cross-kingdom relationships remain poorly defined. Farnesol is a well-known quorum-sensing molecule in Candida, but its ecological roles beyond fungal communication are unclear. Here, we show that Lysobacter enzymogenes directly senses fungal-derived farnesol through the RcsB/C two-component system, which activates the downstream regulator MarR-2 and induces the production of the antifungal metabolite heat-stable antifungal factor (HSAF). This signal hijacking strategy allows L. enzymogenes to convert a fungal communication molecule into a cue that strengthens its antagonistic capacity. We further identify key amino acid residues in RcsC responsible for farnesol recognition, revealing the bacterial two-component system (TCS) known to detect this molecule. These findings expand the functional scope of fungal quorum-sensing signals, uncover a previously unrecognized mechanism of interkingdom antagonism, and provide insights with potential applications in microbiome-based biocontrol.