Halotolerant Bacillus sp. as a source of antifungal agents against major mushroom pathogens

Abstract

The present study focuses on bioprospecting of halotolerant bacteria from a hypersaline environment for antifungal agents against major mushroom pathogens. A total of 20 morphologically different fungi were isolated from composts and infected fruiting bodies of Agaricus bisporus; belonging to the genera Trichoderma, Penicillium, Aspergillus, Mucor and Rhizopus. In addition, 131 halotolerant bacteria out of 280 exhibited antifungal activity against phytopathogens, Trichoderma sp., and Penicillium sp. The isolates (80) showing maximum and consistent activity were screened against the isolated mushroom pathogens, Trichoderma harzianum MTCC 3178 and Lecanicillium fungicola MTCC 2016. About 33.8 percent halotolerant bacteria produced an antifungal metabolite that inhibited the mycelial growth of Trichoderma harzianum MTCC 3178, 20 percent inhibited mycelium growth of Lecanicillium fungicola MTCC 2016, 48.8 percent other Trichoderma spp., 26.3 percent Penicillium spp. and 2.5 percent inhibited Aspergillus spp. The bacterial isolate BGUMS93 showed highest broad spectrum activity against these pathogens. Carbohydrate utilization profile, biochemical characteristics and 16S rRNA gene sequencing revealed BGUMS93 as Bacillus sp. (KC991034.1) with 97 percent similarity to Bacillus subtilis. BGUMS93 produced extracellular antifungal metabolites in butanol extract showing maximum activity against Trichoderma harzianum MTCC 3178 and in chloroform extract against Lecanicillium fungicola MTCC 2016. Thus, Bacillus spp. from Goa's salterns could be a way to provide natural fungicide as an alternative to synthetic fungicides used in mushroom cultivation.