Abstract:
Objective Fermentation process of Bacillus methylotrophicus Z21, which exhibited antifungal activities on Aspergillus niger and Trichoderma koningii among others in a preliminary study, was optimized, and the stability and antibacterial properties of the broth as a nature preservative examined.
Method The fermentation conditions, including temperature, UV, pH, time, enzymes, and metal ions, were optimized based on the antifungal activity of the broth against T. koningii determined by the Oxford cup method. Effects of the ammonium sulfate-precipitated crude extract on the MIC, inhibition rate, spore germination, and hypha growth of T. koningii were also examined.
Result The optimized process was conducted in a 500 mL flask to hold 150 mL liquid medium with 3% inoculum for the 60 h fermentation at 30 ℃ under constant 140 r·min−1 stirring. The inhibition rate of the 150 μL sterile fermentation broth on the hypha growth was 72%. The increased UV absorbances of the T. koningii culture liquid at OD260 and OD280 by the treatment of the extract at MIC of 25 mg·mL−1 indicated a leakage of nucleic acids and proteins into the liquid from the mycelia. The Z21 fermentation broth was resistant to heat, acid, and alkali but insensitive to UV, enzymes, and metal ions. The scanning electron microscopic images showed that the hyphae of T. koningii treated by the broth became slender without spore stems.
Conclusion The growth and reproduction of T. koningii were significantly inhibited by the presence of B. methylotrophicus Z21 fermentation broth. The antifungal activity of the broth remained stable under elevated temperature and/or acidic or alkali conditions.
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