Fermentation conditions for the biocontrol strain HD-087 against cucumber Fusarium wilt and it’s antibacterial effect

Abstract:

[Objective] In order to improve the inhibitory rate of fermentation broth of Streptomyces bikiniensis strain HD-087 against Fusarium oxysporum strain HU-M, the shake-flask fermentation conditions of biocontrol agent HD-087 were optimized. Restraining effectiveness of broth towards HU-M has been tested at the same time. [Methods] The liquid fermentation medium and conditions of HD-087 were optimized by single factor experiments and orthogo-nal experiments. After inoculation with broth, HU-M hyphae morphology and germination of conidia were then examined under the light microscope, and the relative conductivity of HU-M hyphae was measured using a conductivity meter. [Results] The composition of the optimal medium was 1.00% (W/V) starch, 0.80% (W/V) soybean flour, 0.12% (W/V) yeast extract, 0.40% (W/V) CaCO3. The optimal fermentation conditions were the combination of temperature 28 °C, initial pH 6.8, 180 r/min, incubation time 5 d, 1 mL inoculum volume and medium volume 40 mL/250 mL. The result of antibacterial effect can be concluded as follows: abnor-mality of pathogen hyphae and leakage of cytoplasm after treated with broth; meanwhile the inhibitive rate to conidia germination reached 72.1% when the broth diluted by 5 times. In ad-dition to that, exosmosis of hyphae content, conductance rate increased. [Conclusion] All these changes indicate that optimal shake-flask fermentation conditions can improve the in-hibitory activity of HD-087 broth against F. oxysporum HU-M, and the broth has been proved efficient for suppression of HU-M by severely destroying cell membrane structure, it’s of great potential application value.