Genomic Analysis and Secondary Metabolites Production of the Endophytic Bacillus velezensis Bvel1: A Biocontrol Agent against Botrytis cinerea Causing Bunch Rot in Post-Harvest Table Grapes

Abstract

Botrytis bunch rot caused by Botrytis cinerea is one of the most economically significant post-harvest diseases of grapes. In the present study, we showed that the bacterial strain Bvel1 is phylogenetically affiliated to Bacillus velezensis species. The strain Bvel1 and its secreted metabolites exerted an antifungal activity, under in vitro conditions, against B. cinerea. UHPLC–HRMS chemical analysis revealed that iturin A2, surfactin-C13 and -C15, oxydifficidin, bacillibactin, L-dihydroanticapsin, and azelaic acid were among the metabolites secreted by Bvel1. Treatment of wounded grape berries with Bacillus sp. Bvel1 cell culture was effective for controlling grey mold ingress and expansion in vivo. The effectiveness of this biological control agent was a function of the cell culture concentration of the antagonist applied, while preventive treatment proved to be more effective compared to curative. The strain Bvel1 exhibited an adequate colonization efficiency in wounded grapes. The whole-genome phylogeny, combined with ANI and dDDH analyses, provided compelling evidence that the strain Bvel1 should be taxonomically classified as Bacillus velezensis. Genome mining approaches showed that the strain Bvel1 harbors 13 antimicrobial biosynthetic gene clusters, including iturin A, fengycin, surfactin, bacilysin, difficidin, bacillaene, and bacillibactin. The results provide new insights into the understanding of the endophytic Bacillus velezensis Bvel1 biocontrol mechanism against post-harvest fungal pathogens, including bunch rot disease in grape berries.

Genomic and Metabolomic Insights into Secondary Metabolites of the Novel Bacillus halotolerans Hil4, an Endophyte with Promising Antagonistic Activity against Gray Mold and Plant Growth Promoting Potential

“…It was also recently found that supernatant from Pseudomonas syringae contains azelaic acid, suggesting a role in plant-bacteria communication [60]. The first report of azelaic acid production from Bacillus species was in a study of B. velezensis Bvel1 that also examined ethyl acetate extracts containing secreted agar-diffusible metabolites from singly grown bacterial solid culture [15], as in the present study.…”

“…Endophytic bacteria can combat pathogens by space occupation, production of lytic enzymes, and antifungal secondary metabolites [10,11], as well as through the activation of plant defense [12]. Studies regarding the biological control ability of bacteria in fruit or leaves are emerging in the literature for B. velezensis, B. amyloliquefaciens and B. subtilis strains [13][14][15][16][17]; however, studies for B. haloterans strains remain scarce [18][19][20].…”

Integrated Genomic and Metabolomic Analysis Illuminates Key Secreted Metabolites Produced by the Novel Endophyte Bacillus halotolerans Cal.l.30 Involved in Diverse Biological Control Activities

“…One of the most significant compounds secreted and identified in B. halotolerans Cal.l.30 is the active substance azelaic acid (AzA). Thus far, only a few reports have been found on the biosynthesis of AzA by bacteria, and only two by Bacillus species and, specifically, B. velezensis Bvel1 and B. halotolerans Hil4 [18,26,56]. AzA is a nine-carbon dicarboxylic acid, which has been reported primarily in plants as a mobile signaling molecule that activates plant defense mechanisms [85].…”

Mechanisms of Action of Microbial Biocontrol Agents against Botrytis cinerea

“…Some of the most well-known members are enterobactin produced by E. coli, pyochelin produced by P. aeruginosa, salmochelin produced by Salmonella enterica, bacillibactin produced by Bacillus spp., agrobactin produced by Agrobacterium tumefaciens, parabactin produced by Paracoccus denitrificans, and azotobactin produced by Azotobacter vinelandii [107,124]. Members of Bacillus have been studied for their ability to produce siderophore-mediated antifungal activity by producing bacillibactin, which inhibits fungal growth against some pathogenic fungi, such as Macrophomina phaseolina, Fusarium moniliforme, and B. cinerea [73,[125][126][127]. Moreover, P. aeruginosa 7NSK has a protective effect against B. cinerea when pyochelin and pyocyanin are produced together and when pyoverdine is produced, in tomato plants and Arabidopsis thaliana, respectively [77,128].…”