A Crosstalk Between Brachypodium Root Exudates, Organic Acids, and Bacillus velezensis B26, a Growth Promoting Bacterium

Abstract

Plant growth-promoting rhizobacteria (PGPR) are associated with plant roots and use organic compounds that are secreted from root exudates as food and energy source. Root exudates can chemoattract and help bacteria to colonize the surface of plant roots by inducing chemotactic responses of rhizospheric bacteria. In this study, we show that root colonization of Brachypodium distachyon by Bacillus velezensis strain B26 depends on several factors. These include root exudates, organic acids, and their biosynthetic genes, chemotaxis, biofilm formation and the induction of biofilm encoding genes. Analysis of root exudates by GC-MS identified five intermediates of the TCA cycle; malic, fumaric, citric, succinic, oxaloacetic acids, and were subsequently evaluated. The strongest chemotactic responses were induced by malic, succinic, citric, and fumaric acids. In comparison, the biofilm formation was induced by all organic acids with maximal induction by citric acid. Relative to the control, the individual organic acids, succinic and citric acids activated the epsD gene related to EPS biofilm, and also the genes encoding membrane protein ( yqXM ) and hydrophobin component ( bslA ) of the biofilm of strain B26. Whereas epsA and epsB genes were highly induced genes by succinic acid. Similarly, concentrated exudates released from inoculated roots after 48 h post-inoculation also induced all biofilm-associated genes. The addition of strain B26 to wild type and to icdh mutant line led to a slight induction but not biologically significant relative to their respective controls. Thus, B26 has no effect on the expression of the ICDH gene, both in the wild type and the mutant backgrounds. Our results indicate that root exudates and individual organic acids play an important role in selective recruitment and colonization of PGPR and inducing biofilm. The current study increases the understanding of molecular mechanisms behind biofilm induction by organic acids.

Bacillus velezensis strain B26 modulates the inflorescence and root architecture of Brachypodium distachyon via hormone homeostasis

“…A Semi-hydroponics system was developed for scanning of roots using Magenta GA-7 tissue culture boxes that were filled with sterile glass low alkali beads (Ceroglass, USA) saturated with Hoagland’s solution as fully described in Sharma et al . 5 . Pre-germinated seeds of wild type Bd21-3, transgenic lines UBI:FT1 and UBI:VRN1 (6 seeds/box) were transferred to Magenta boxes where each box is an experimental unit.…”

“…The conditions for qRT-PCR were adjusted for each primer set. PCR amplification was performed in a 10 µL reaction following the protocol of Sharma et al 5 . The 2 −ΔΔ C T method 52 was applied to normalize the target gene over the housekeeping genes UBC18 .…”

“…We also showed that strain B26 improves the growth of these grasses under extended drought conditions by modulating the expression of drought-responsive genes in B. distachyon, and also by the modification of osmolytes in roots and shoots of timothy grass 3 . Successful colonization of B. distachyon roots by strain B26 is based on the composition of roots exudates (the type of organic acid and their biosynthetic genes), chemotaxis and the induction of biofilm and their encoding genes 5 .…”

Plant–Microbiome Crosstalk: Dawning from Composition and Assembly of Microbial Community to Improvement of Disease Resilience in Plants

“…Usually, polysaccharides are secreted by root tips and abundantly present in root caps and mucilage [50]. However, elongation zones and meristem contain oxidized compounds such as amino acids, sugars, and organic acids [51,52].…”

Citric Acid in Rice Root Exudates Enhanced the Colonization and Plant Growth-Promoting Ability of Bacillus altitudinis LZP02

“…Organic acids and amino acids are the main components of primary metabolites in root exudates and are secreted and passively lost from roots ( 7 ). A previous study has shown that chemotactic responses of Bacillus velezensis B26 were induced by organic acids and citric acids enhanced the gene expression connected to the biofilm ( 8 ). Another study demonstrated that Escherichia coli and Bacillus subtilis movement toward amino acids can be utilized quickly ( 9 ).…”