Chemotaxis of Beneficial Rhizobacteria to Root Exudates: The First Step towards Root–Microbe Rhizosphere Interactions

Abstract

Chemotaxis, the ability of motile bacteria to direct their movement in gradients of attractants and repellents, plays an important role during the rhizosphere colonization by rhizobacteria. The rhizosphere is a unique niche for plant–microbe interactions. Root exudates are highly complex mixtures of chemoeffectors composed of hundreds of different compounds. Chemotaxis towards root exudates initiates rhizobacteria recruitment and the establishment of bacteria–root interactions. Over the last years, important progress has been made in the identification of root exudate components that play key roles in the colonization process, as well as in the identification of the cognate chemoreceptors. In the first part of this review, we summarized the roles of representative chemoeffectors that induce chemotaxis in typical rhizobacteria and discussed the structure and function of rhizobacterial chemoreceptors. In the second part we reviewed findings on how rhizobacterial chemotaxis and other root–microbe interactions promote the establishment of beneficial rhizobacteria-plant interactions leading to plant growth promotion and protection of plant health. In the last part we identified the existing gaps in the knowledge and discussed future research efforts that are necessary to close them.

Plant Growth-Promoting Activity of Bacteria Isolated from Asian Rice (Oryza sativa L.) Depends on Rice Genotype

“…Of the five isolates tested, two (n00163 and n00167) shared similar phenotypic carbon source usage characteristics (Table S8). Of the different metabolic phenotypes, methyl pyruvate is a plant chemoeffector ( 31 ) and glycerol is a leaf exudate as a result of carbon dioxide fixation in photosynthesis ( 32 ). Glycerol was not used by n00132, while methyl pyruvate was not used by n00132 and n00172.…”

Taxonomic and Functional Diversity of Rhizosphere Microbiome Recruited From Compost Synergistically Determined by Plant Species and Compost

“…These results suggested that microorganisms with the ability to sense and uptake these substances with small molecular weight might be competent in the rhizosphere. Indeed, wide taxa of rhizosphere bacteria such as Pseudomonas and Bacillus can sense carboxylic acids and amino acids, which may stimulate bacterial mobility ( Taguchi et al, 1997 ; Alvarez-Ortega and Harwood, 2007 ; Sampedro et al, 2015 ; Feng et al, 2021 ). An increase of functional traits associated with amino acid competition indicated a fascinating relationship between plant and rhizosphere microorganisms in terms of N-exchanging.…”

Plant-Microbe Interaction in Sustainable Agriculture: The Factors That May Influence the Efficacy of PGPM Application

“…Root exudates modulate the composition of the microbial community in the rhizosphere, i.e., the soil influenced by plant roots [103,104]. The persistence of a bacterial population in the rhizosphere depends in part on its chemotaxis toward different components secreted by the roots as well as its ability to use them as substrates [105][106][107][108]. The possibility of moving in the soil, and thus the presence of flagella in bacterial species, are characteristics necessary to reach the root and, therefore, influence the nodulation [109].…”