Identification of Pyrrole-2-Carboxylic Acid from the Biocontrol Agent Lysobacter Involved in Interactions with Fusarial Fungi

Lysobacter, a genus of Gram-negative bacteria, is known for producing antibiotic compounds, making it a promising biocontrol agent against crop pathogens. As part of the soil microbiome, Lysobacter species cooccur with a variety of microorganisms in the ecosystem. However, little is known about bioactive natural products involved in Lysobacter’s interactions with other organisms. This study investigated interactions between Lysobacter sp. 3655 and two economically important fungal pathogens, Fusarium graminearum and Fusarium verticillioides. We discovered a Lysobacter molecule that is dramatically suppressed when co-culturing with the fungi, and the structure of this molecule was determined to be pyrrole-2-carboxylic acid (P2C). Chitin, a primary component of fungal cell walls, also suppressed P2C production in Lysobacter. Exogenous P2C addition promoted formation of Lysobacter biofilms within a range of concentrations, suggesting its potential role as a signaling molecule. Previously reported result showed that the mutation of the global regulator Clp in Lysobacter enzymogenes led to drastic increase of biofilm formation. Intriguingly, while P2C increased the biofilm formation in the wildtype of L. enzymogenes, it reduced the biofilms in the Clp mutant. Together, these findings reveal P2C as a novel signaling molecule mediating the interaction between Lysobacter and surrounding fungal species, highlighting its role in Lysobacter adaptation in response to environmental conditions.