-Encoding Protein Is the Only Chemoreceptor That Regulates Chemoattraction toward the Broad Antibacterial Agent Formic Acid

Soil-born plant pathogens, especially , generally navigate their way to hosts through recognition of the root exudates by chemoreceptors. However, there is still a lack of appropriate identification of chemoreceptors and their ligands in . Here, Atu0526, a sCache-type chemoreceptor from C58, was confirmed as the receptor of a broad antibacterial agent, formic acid. The binding of formic acid to Atu0526 was screened using a thermo shift assay and verified using isothermal titration calorimetry. Inconsistent with the previously reported antimicrobial properties, formic acid was confirmed to be a chemoattractant to and could promote its growth. The chemotaxis of C58 toward formic acid was completely lost with the knock-out of , and regained with the complementation of the gene, indicating that Atu0526 is the only chemoreceptor for formic acid in C58. The affinity of formic acid to Atu0526 significantly increased after the arginine at position 115 was replaced by alanine. However, in vivo experiments showed that the R115A mutation fully abolished the chemotaxis of toward formic acid. Molecular docking based on a predicted 3D structure of Atu0526 suggested that the arginine may provide "an anchorage" for formic acid to pull the minor loop, thereby forming a conformational change that generates the ligand-binding signal. Collectively, our findings will promote an understanding of sCache-type chemoreceptors and their signal transduction mechanism.