Abstract
BackgroundBacillus velezensis is an endospore-forming, free-living soil bacterium with potential as a biopesticide against a broad spectrum of microbial pathogens of plants. Its potential for commercial development is enhanced by rapid replication and resistance to adverse environmental conditions, typical of Bacillus species. However, the use of beneficial microbes against phytopathogens has not gained dominance due to limitations that may be overcome with new biopesticidal strains and/or new biological knowledge.ResultsHere, we isolated B. velezensis strain 9D-6 and showed that it inhibits the in vitro growth of prokaryotic and eukaryotic pathogens, including the bacteria Bacillus cereus, Clavibacter michiganensis, Pantoea agglomerans, Ralstonia solanacearum, Xanthomonas campestris, and Xanthomonas euvesicatoria; and the fungi Alternaria solani, Cochliobolus carbonum, Fusarium oxysporum, Fusarium solani, Gibberella pulicaris, Gibberella zeae, Monilinia fructicola, Pyrenochaeta terrestris and Rhizoctonia solani. Antimicrobial compounds with activity against Clavibacter michiganensis were isolated from B. velezensis 9D-6 and characterized by high resolution LC-MS/MS, yielding formulae of C52H91N7O13 and C53H93N7O13, which correspond to [Leu7] surfactins C14 and C15 (also called surfactin B and surfactin C), respectively. We further sequenced the B. velezensis 9D-6 genome which consists of a single circular chromosome and revealed 13 gene clusters expected to participate in antimicrobial metabolite production, including surfactin and two metabolites that have not typically been found in this species - ladderane and lantipeptide. Despite being unable to inhibit the growth of Pseudomonas syringae DC3000 in an in vitro plate assay, B. velezensis 9D-6 significantly reduced root colonization by DC3000, suggesting that 9D-6 uses methods other than antimicrobials to control phytopathogens in the environment. Finally, using in silico DNA-DNA hybridization (isDDH), we confirm previous findings that many strains currently classified as B. amyloliquefaciens are actually B. velezensis.ConclusionsThe data presented here suggest B. velezensis 9D-6 as a candidate plant growth promoting bacterium (PGPB) and biopesticide, which uses a unique complement of antimicrobials, as well as other mechanisms, to protect plants against phytopathogens. Our results may contribute to future utilization of this strain, and will contribute to a knowledge base that will help to advance the field of microbial biocontrol.
Highlights
Bacillus velezensis is an endospore-forming, free-living soil bacterium with potential as a biopesticide against a broad spectrum of microbial pathogens of plants
We identified antimicrobial compounds produced by B. velezensis 9D-6 as bacterial cyclic lipopeptides [Leu7] surfactin C14 and [Leu7] surfactin C15
Zones of microbial inhibition on solid medium around discs inoculated with 9D-6 indicated that it inhibits growth of the Gram positive bacteria Bacillus cereus and Clavibacter michiganensis; and of the Gram negative bacteria Pantoea agglomerans, Ralstonia solanacearum, Xanthomonas campestris, and Xanthomonas euvesicatoria; but not Erwinia amylovora or Pseudomonas syringae DC3000
Summary
Bacillus velezensis is an endospore-forming, free-living soil bacterium with potential as a biopesticide against a broad spectrum of microbial pathogens of plants. While synthetic pesticides, including bactericides and fungicides, can be effective, the reliance on synthetic inputs in modern agriculture can cause serious environmental problems by affecting soil fertility, the development of insect resistance, and bioaccumulation of toxic residues in wildlife, livestock, and humans [1]. Such concerns have prompted research into alternative, sustainable strategies to manage plant pests and diseases. Since biopesticides are derived from natural microorganisms, they are often less toxic and affect fewer non-target organisms compared with synthetic pesticides They can be effective in small quantities and are biodegradable, largely avoiding pollution problems. Biopesticides are promising in promoting agricultural sustainability and intensification, helping to meet today’s complex challenges
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