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

<i>Lysobacter</i>, 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, <i>Lysobacter</i> species cooccur with a variety of microorganisms in the ecosystem. However, little is known about bioactive natural products involved in <i>Lysobacter</i>'s interactions with other organisms. This study investigated interactions between <i>Lysobacter</i> sp. 3655 and two economically important fungal pathogens, <i>Fusarium graminearum</i> and <i>Fusarium verticillioides</i>. We discovered a <i>Lysobacter</i> 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 <i>Lysobacter</i>. Exogenous P2C addition promoted formation of <i>Lysobacter</i> 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 <i>Lysobacter enzymogenes</i> led to drastic increase of biofilm formation. Intriguingly, while P2C increased the biofilm formation in the wildtype of <i>L. enzymogenes</i>, it reduced the biofilms in the Clp mutant. Together, these findings reveal P2C as a novel signaling molecule mediating the interaction between <i>Lysobacter</i> and surrounding fungal species, highlighting its role in <i>Lysobacter</i> adaptation in response to environmental conditions.