Agrobacterium fabrum atu0526-Encoding Protein Is the Only Chemoreceptor That Regulates Chemoattraction toward the Broad Antibacterial Agent Formic Acid

Abstract

Soil-born plant pathogens, especially Agrobacterium, 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 Agrobacterium. Here, Atu0526, a sCache-type chemoreceptor from Agrobacterium fabrum 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 A. fabrum and could promote its growth. The chemotaxis of A. fabrum C58 toward formic acid was completely lost with the knock-out of atu0526, and regained with the complementation of the gene, indicating that Atu0526 is the only chemoreceptor for formic acid in A. fabrum C58. The affinity of formic acid to Atu0526LBD 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 A. fabrum 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.

Metabolism-linked methylotaxis sensors responsible for plant colonization in Methylobacterium aquaticum strain 22A

“…Strain 22A did not exhibit any taxis toward 2 and 0.2% formate that is also a metabolite in methylotrophic pathway (data not shown), although formate serves as a chemoattractant for a soil plant pathogen, Agrobacterium fabrum strain C58 ( Wang et al, 2021 ).…”

The dCache Domain of the Chemoreceptor Tlp1 in Campylobacter jejuni Binds and Triggers Chemotaxis toward Formate

“…To our knowledge, C. jejuni Tlp1 is the first discovered chemoreceptor with a dCache domain that directly binds to formate with high specificity and elicits the strong chemotaxis of bacteria. The sCache chemoreceptor Atu0526 from A. fabrum C58 was reported to bind formate directly ( 32 ), but the residues in the binding pocket interacting with formate are different from those in the pocket of the dCache domain of C. jejuni Tlp1. A novel aspect of this study is that formate binds to the membrane-proximal subdomain of dCache.…”

“…It could not trigger chemotaxis until the concentration of formate reached 100 mM, indicating that formate is not a primary ligand of McpV and is an inefficient chemoattractant for S. meliloti ( 31 ). Until now, the chemoreceptor Atu0526 with an sCache LBD from Agrobacterium fabrum C58 was the only receptor that was reported to bind formate with higher affinity ( K d = 172 μM) and trigger chemotaxis ( 32 ).…”

An aerotaxis receptor influences invasion of Agrobacterium tumefaciens into its host

“…Large numbers of chemoreceptors in A. tumefaciens suggest that the bacteria can detect diverse chemical molecules or environmental stimuli to navigate the way to favorable ecological niches ( Xu et al., 2020 ). To date, the identification of chemoreceptors in A. tumefaciens has been limited to only four ( Shi et al., 2017 ; Wang et al., 2021 ; Ye et al., 2021 ; Zong et al., 2022 ). In the case of A. tumefaciens C58, Atu0514, which is predicted to possess a globin domain as its LBD, has been implicated in the chemotactic response to sucrose, valine, citric acid, and acetosyringone (AS) ( Ye et al., 2021 ).…”

“…In the case of A. tumefaciens C58, Atu0514, which is predicted to possess a globin domain as its LBD, has been implicated in the chemotactic response to sucrose, valine, citric acid, and acetosyringone (AS) ( Ye et al., 2021 ). Atu0526 has been found to use a single-Cache domain as LBD to bind the broad antibacterial agent formic acid ( Wang et al., 2021 ). Additionally, Atu1912, another chemoreceptor featuring a single-Cache domain, has been shown to mediate the attractant response to pyruvate and the repellent response to propionic acid.…”