Abstract
BackgroundMicroorganisms, including Bacillus species are used to help control plant pathogens, thereby reducing reliance on synthetic pesticides in agriculture. Bacillus velezensis strain 1B-23 has been shown to reduce symptoms of bacterial disease caused by Clavibacter michiganensis subsp. michiganensis in greenhouse-grown tomatoes, with in vitro studies implicating the lipopeptide surfactin as a key antimicrobial. While surfactin is known to be effective against many bacterial pathogens, it is inhibitory to a smaller proportion of fungi which nonetheless cause the majority of crop diseases. In addition, knowledge of optimal conditions for surfactin production in B. velezensis is lacking.ResultsHere, B. velezensis 1B-23 was shown to inhibit in vitro growth of 10 fungal strains including Candida albicans, Cochliobolus carbonum, Cryptococcus neoformans, Cylindrocarpon destructans Fusarium oxysporum, Fusarium solani, Monilinia fructicola, and Rhizoctonia solani, as well as two strains of C. michiganensis michiganensis. Three of the fungal strains (C. carbonum, C. neoformans, and M. fructicola) and the bacterial strains were also inhibited by purified surfactin (surfactin C, or [Leu7] surfactin C15) from B. velezensis 1B-23. Optimal surfactin production occurred in vitro at a relatively low temperature (16 °C) and a slightly acidic pH of 6.0. In addition to surfactin, B. velenzensis also produced macrolactins, cyclic dipeptides and minor amounts of iturins which could be responsible for the bioactivity against fungal strains which were not inhibited by purified surfactin C.ConclusionsOur study indicates that B. velezensis 1B-23 has potential as a biocontrol agent against both bacterial and fungal pathogens, and may be particularly useful in slightly acidic soils of cooler climates.
Highlights
Microorganisms, including Bacillus species are used to help control plant pathogens, thereby reducing reliance on synthetic pesticides in agriculture
Pathogen inhibition was tested in a similar way using filter discs inoculated with a crude extract of hydrophobic metabolites that were isolated from B. velezensis Bacillus velezensis strain 1B-23 (1B-23), rather than with the organism itself
Here, we showed that B. velezensis 1B-23 exhibits a high degree of inhibition against phylogenetically diverse fungal pathogens, and that some of this inhibition can be attributed to surfactin
Summary
Microorganisms, including Bacillus species are used to help control plant pathogens, thereby reducing reliance on synthetic pesticides in agriculture. Bacillus velezensis strain 1B-23 has been shown to reduce symptoms of bacterial disease caused by Clavibacter michiganensis subsp. While surfactin is known to be effective against many bacterial pathogens, it is inhibitory to a smaller proportion of fungi which cause the majority of crop diseases. An increasing burden is being placed on agricultural industries to sustain earth’s rapidly growing population [1, 2]. One opportunity for increasing or maintaining production from existing land is to target plant pathogens that lead to disease in crops or in the humans or animals that consume them. By preventing and controlling agricultural disease, farmers can limit crop waste while maximizing their yields [3]. Researchers and farmers are seeking more ecofriendly methods to prevent these issues
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