Stereoisomers of Nonvolatile Acetylbutanediol Metabolites Produced by Bacillus velezensis WRN031 Improved Root Elongation of Maize and Rice.

Abstract

Inoculation of crop plants with strains of beneficial bacteria can result in promotion of plant growth. In our study, we demonstrated that Bacillus velezensis WRN031 as a plant-growth-promoting rhizobacteria (PGPR) improved the maize seedling growth following inoculation with WRN031. Fluorescence microscopy visualization indicated that GFP-labeled B. velezensis WRN031 had accumulated on the maturation zones of both primary and lateral roots of maize. Two metabolites were detected in the rhizosphere soil of maize root inoculation with WRN031 using HPLC-DAD analyses. Through guided isolation from an ethyl acetate extract of B. velezensis WRN031, these two nonvolatile meso stereoisomers 3S,4R-acetylbutanediol (3S,4R-ABD, 1) and 3R,4R-acetylbutanediol (3R,4R-ABD, 2) were identified and found to occur at a ratio of 1:2 (v/v) in maize rhizosphere soil. Bioactivity screening indicated that compounds 1 and 2, as well as a v/v = 1:2 mixture of both 1 and 2, significantly improved the root elongation of both maize and rice, with the effective enhancement concentration related to their concentration in rhizosphere soil. These results suggested that 3S,4R-ABD and 3R,4R-ABD produced by B. velezensis WRN031 might improve the growth of their host plants and provides evidence that nonvolatiles accumulating in the root maturation zone may regulate the relationship between roots and beneficial bacteria.