Bacillus velezensis: A Valuable Member of Bioactive Molecules within Plant Microbiomes

Abstract

Bacillus velezensis is an aerobic, gram-positive, endospore-forming bacterium that promotes plant growth. Numerous strains of this species have been reported to suppress the growth of microbial pathogens, including bacteria, fungi, and nematodes. Based on recent phylogenetic analysis, several Bacillus species have been reclassified as B. velezensis. However, this information has yet to be integrated into a well-organized resource. Genomic analysis has revealed that B. velezensis possesses strain-specific clusters of genes related to the biosynthesis of secondary metabolites, which play significant roles in both pathogen suppression and plant growth promotion. More specifically, B. velezensis exhibits a high genetic capacity for synthesizing cyclic lipopeptides (i.e., surfactin, bacillomycin-D, fengycin, and bacillibactin) and polyketides (i.e., macrolactin, bacillaene, and difficidin). Secondary metabolites produced by B. velezensis can also trigger induced systemic resistance in plants, a process by which plants defend themselves against recurrent attacks by virulent microorganisms. This is the first study to integrate previously published information about the Bacillus species, newly reclassified as B. velezensis, and their beneficial metabolites (i.e., siderophore, bacteriocins, and volatile organic compounds).

Keywords: Bacillus velezensis; bioactive compound; induced systemic resistance; volatile organic compound.

Figure 1

Bacillus velezensis is the conspecific species integrating B. amyloliquefaciens subsp. plantarum and B. methylotrophicus (adapted by Dunlap et al. [22]). The significance of the numbers are explained at the bottom of the same column.

Figure 2

Phylogenetic tree constructed from the rpoB gene sequences of type strains of species from the “B. subtilis species complex” by the neighbor-joining method (using MEGA software). Bootstrap values (%) are given at the nodes obtained by repeating the analysis 1000 times. The scale bar indicates 0.02 nucleotide substitutions per nucleotide position.

Figure 3

Molecular structure of ribosomal and nonribosomal bioactive compounds synthesized by B. velezensis.

Figure 4

Signal transduction pathway of induced systemic resistance stimulated by B. velezensis. NPR1: non-expressor of PR1; JA/ET: the jasmonic acid/ethylene signaling pathways; SA: Salicylic Acid.