Recognition of dominant attractants by key chemoreceptors mediates recruitment of plant growth‐promoting rhizobacteria

Abstract

Summary Chemotaxis to plant root exudates is supposed to be a prerequisite for efficient root colonization by rhizobacteria. This is a highly multifactorial process since root exudates are complex compound mixtures of which components are recognized by different chemoreceptors. Little information is available as to the key components in root exudates and their receptors that drive colonization related chemotaxis. We present here the first global assessment of this issue using the plant growth‐promoting rhizobacterium (PGPR) Bacillus velezensis SQR9 (formerly B. amyloliquefaciens). This strain efficiently colonizes cucumber roots, and here, we show that chemotaxis to cucumber root exudates was essential in this process. We conducted chemotaxis assays using cucumber root exudates at different concentrations, individual exudate components as well as recomposed exudates, taking into account their concentrations detected in root exudates. Results indicated that two key chemoreceptors, McpA and McpC, were essential for root exudate chemotaxis and root colonization. Both receptors possess a broad ligand range and recognize most of the exudate key components identified (malic, fumaric, gluconic and glyceric acids, Lys, Ser, Ala and mannose). The remaining six chemoreceptors did not contribute to exudate chemotaxis. This study provides novel insight into the evolution of the chemotaxis system in rhizobacteria.

A predatory myxobacterium controls cucumber Fusarium wilt by regulating the soil microbial community

“…Many studies have shown that chemotaxis towards root exudates is the first step of bacterial colonization of roots [49]. Organic acids, amino acids, sugars, quaternary ammonium salts, and secondary metabolites secreted by plants are all potential chemoattractants for beneficial bacteria [49][50][51][52]. Our results showed that strain EGB could also be attracted by root exudates.…”

“…We speculate that root exudates of cucumbers attracted the movement of strain EGB in the soil. Many studies have shown that chemotaxis towards root exudates is the first step of bacterial colonization of roots [49]. Organic acids, amino acids, sugars, quaternary ammonium salts, and secondary metabolites secreted by plants are all potential chemoattractants for beneficial bacteria [49][50][51][52].…”

“…Maltose and maltitol were the most efficient chemoattractants, attracting strain EGB at low concentrations (10 μM). Maltose has been determined to be an important compound in the root exudates of cucumbers [49,53] and other plants [54]. Although chemotaxis of myxobacteria towards small soluble chemicals is doubtful [55,56], chemotaxis driven by pili-based single-cell "twitching motility" has been shown to be important in the biofilm development of Pseudomonas aeruginosa [57].…”

Pectin induced colony expansion of soil-derived Flavobacterium strains

“…Bacterial colonization of plant roots is a multi-stage process that involves recognition, movement towards attractants and attachment (15). Once attached, persistence and propagation on plant roots is dependent on metabolic fitness (52,53), resistance to plant protective mechanisms and inter-microbial interactions.…”

Framework for Quantification of the Dynamics of Root Colonization by Pseudomonas fluorescens Isolate SBW25

“…Plants and microorganisms secrete a broad range of chemical compounds which can impact bacterial growth and alter their physiology (Dennis et al, 2010;Yu et al, 2019). Plants are known to recruit certain bacteria while suppressing others through immune responses (Chowdhury et al, 2015;Feng et al, 2019). Differences in community structure are observed at different stages of root development, or depending on root anatomy (Humphris et al, 2005;Schmidt et al, 2018).…”