In a previously study, the Bacillus sp. strain IA was successfully isolated with high sensitivity to rice husk biochar (RHB). Moreover, RHB promoted an antibiotic iturin A production by strain IA. In order to develop the biocontrol agent, we attempted to reveal the functions of the RHB in promoting the production of iturin A by strain IA. The promotion effects of growth, sporulation and iturin A production of strain IA by the RHB were explained as follows. First, the manganese ion, released from RHB, promoted the sporulation and iturin A production of strain IA. Second, the silicon dioxide contained in RHB adsorbed the metabolic inhibitor(s) and promoted the iturin A production of strain IA. Finally, the combination of manganese ion and silicon dioxide promoted the growth, sporulation and iturin A production of the Bacillus sp. strain IA. To culture strain IA in the medium combining manganese ion and silicon dioxide, the total cells, spore cells and iturin A production increased 15 times, 10,000 times and 18 times higher than the control medium, respectively.
The purpose of this study is to isolate the beneficial microorganisms whose growth is promoted in the presence of charcoal materials. We successfully isolated strain IA, whose growth is promoted on an agar plate with charcoal materials, and identified it as a novel strain of the Bacillus sp. The growth of strain IA in the liquid medium was promoted by the addition of both activated charcoal (AC) and rice husk biochar (RHB). Moreover, the sporulation of strain IA in the RHB medium and the antifungal activity of the culture supernatant of the RHB medium were much higher than those with AC. HPLC and MS analyses revealed that strain IA produced an antifungal lipopeptide iturin A, and the yield of iturin A in the RHB medium was 8 times higher than that in the medium without RHB. This is the first paper to describe the positive effect of RHB on microbial metabolisms.
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