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Genomic analysis of Bacillus subtilis OH 131.1 and co-culturing with Cryptococcus flavescens for control of Fusarium head blight

Christopher A. Dunlap, David A. Schisler, Michael J. Bowman, Alejandro P. Rooney
Plant gene 2015 v.2 pp. 1-9
Bacillus subtilis subsp. subtilis, Cryptococcus flavescens, Fusarium graminearum, Fusarium head blight, antagonists, antifungal properties, biological control, coculture, disease control, fungal antagonists, genes, genomics, greenhouses, high performance liquid chromatography, inoculum, mass spectrometry, metabolites, phylogeny, plant pathogens, sequence analysis, strains, wheat, yeasts
Bacillus subtilis OH 131.1 is a bacterial antagonist of Fusarium graminearum, a plant pathogen which causes Fusarium head blight in wheat. The genome of B. subtilis OH 131.1 was sequenced, annotated and analyzed to understand its potential to produce bioactive metabolites. The analysis identified 6 synthetic clusters for metabolites that could impact biocontrol efficacy. Five of the clusters were confirmed functional with HPLC–MS/MS of the culture supernatant. The analysis also provided the data to determine the phylogeny of the subject strain. The phylogeny results characterize the strain as B. subtilis subsp. subtilis. Comparative genomics was used to compare the genome of B. subtilis OH 131.1 with closely related strains. Previously, the culture supernatant of B. subtilis OH 131.1 showed no antifungal activity, which suggested that it may be a suitable candidate to combine with a yeast antagonist (Cryptococcus flavescens OH 182.9) of Fusarium head blight for possible enhanced biocontrol efficacy. Co-cultures of B. subtilis OH 131.1 and C. flavescens OH 182.9 were produced with varying ratios of the starting inoculum of the two strains. The strains alone and the various ratios were evaluated for biocontrol activity in greenhouse assays. Co-cultures of B. subtilis OH 131.1 and C. flavescens OH 182.9 initially inoculated at a ratio of 1:100 or 1:10, respectively, were the most effective in reducing disease symptoms compared to the control. The most effective co-cultures were not statistically more efficacious than individual strains. This study reports the first co-culturing of bacterial and yeast biocontrol antagonists and their efficacy in greenhouse assays.