Root exudates and chemotactic strains mediate bacterial community assembly in the rhizosphere soil of Casuarina equisetifolia L

Abstract

Rhizosphere bacterial diversity and community structure are important factors involving in plant growth. However, the exact process of how plant rhizosphere bacterial community structures is assembled remains unclear. To investigate the role of bacterial chemotaxis to rhizosphere secretions in the establishment of rhizosphere microbial community in Casuarina equisetifolia, we screened bacteria strains derived from the rhizosphere of Casuarina equisetifolia L. using top three chemicals of the plant root exudates (2,4-di-tert-butylphenol, methyl stearate, and arginine) as chemoattractant. Among 72 bacterial strains, five showed strong chemotaxis to 2,4-di-tert-butylphenol, six to methyl stearate, and eleven to arginine, with the highest bacterial chemotaxis occurring at a concentration of 60 μM. This indicates that arginine is a more important chemoattractant than 2,4-di-tert-butylphenol, methyl stearate in the establishment of rhizosphere microbial community in Casuarina equisetifolia. Bacterial community assembly analysis using different chemoattractants and chemoattractants-plus-bacteria combinations were then performed by burying laboratory prepared bags of sterlized soil into C. equisetifolia forest. Bacteria diversity and enrichment analyses using 16S rDNA sequencing at 7 and 14 days after burying showed that arginine-plus-Ochrobactrum sp. and Pantoea sp. treatment exhibited the greatest similarity to the natural forest bacterial community. Our date provides new insights into how chemoattractants and chemotactic bacteria strains shape the rhizosphere microbial community of C. equisetifolia, which constitutes foundational information for future management of these communities.

Is allelochemical synthesis in Casuarina equisetifolia plantation related to litter microorganisms?

“…Meanwhile, low concentrations of 2,4-DTBP (60 mM) can aggregate rhizosphere soil bacteria, e.g., Bacillus cereus strain CP1, Pseudomonas sp. and Enterobacter hormaechei strain AMS-38 (Huang et al, 2018;Lin et al, 2022). Cui et al (2022) also found that microbial biomass was stimulated with the addition of 0.5 mM 2,4-DTBP and inhibited with the addition of 2.0 mM 2,4-DTBP.…”

“…Meanwhile, low concentrations of 2,4-DTBP (60 μM) can aggregate rhizosphere soil bacteria, e.g., Bacillus cereus strain CP1, Pseudomonas sp. and Enterobacter hormaechei strain AMS-38 ( Huang et al., 2018 ; Lin et al., 2022 ). Cui et al.…”

Certain Tomato Root Exudates Induced by Pseudomonas stutzeri NRCB010 Enhance Its Rhizosphere Colonization Capability

“…Certain root exudate metabolites change the PGPR growth, swarming, and biofilm formation. 2,4-Di-tert-butylphenol and methyl stearate showed strong chemotaxis in the rhizosphere bacteria of Casuarina equisetifolia L. [ 10 ]. In this study, methyl stearate and 2,4-di-tert-butylphenol promoted NRCB010 swarming ( Figure 3 C), which confirms previous results.…”

“…Colonization, chemotaxis, and biofilm formation by PGPR are induced by the root exudates and certain metabolites [ 3 , 5 , 10 ]. Root exudates are composed of low-molecular-weight carbon compounds that are passively or actively exuded from plant roots.…”

“…In addition, palmitic acid, 2-methylbutyric acid, stearic acid, and oleic acid favor PGPR mobility, chemotaxis, and attachment to the roots [ 15 ]. Furthermore, 2,4-di-tert-butylphenol and methyl stearate affect the growth and chemotaxis of microorganisms [ 10 , 16 ].…”