Study On Amino Acids Addition And Response Surface Methodology For Improving Antifungal Substance Production Of Streptomyces Lydicus

In this paper, amino acids addition, UV mutagenesis and response surfacemethodology were used to improve Streptomyces lydicus antifungal activity.Different concentrations of isoleucine (Ile), valine (Val), glutamate (Glu) andproline (Pro) were external added into the fermentation of E9. The results showthat100mg/L Pro addition increased the antifungal activity by7.95%. But Glu, Ileand Val external addition could reduce the production of the antifungal substances.While, Glu and Pro increased streptolydigin production of S. lydicus E9by73.33%and32.75%respectively. In the opposite, Val and Ile inhibit the biosynthesis ofstreptolydigin.UV mutagenesis and agar block were used to screen higher producing S. lydicusstrain. A good stability overproducing strain E12was obtained and its inhibition ratewas8.78%higher than the E9. Also, high-yielding strain E12with a strong growthinhibition to other pathogenic funguses.In order to enhance the inhibition, response surface methodology was used formedium optimization. Starch, soybean meal, K2HPO43H2O and MgSO47H2Owere determined as the main factors influence antifungal activity of E12bysingle-factor method in the medium composition optimization, with their optimalconcentration were also confirmed. BBD experimental optimization, which designedby Design-Expert.V8.0.6.1software, analysis showed that the relationship betweenthe four factors closer to quadratic polynomial model and A, C, D, A2, B2, C2aresignificant model termsin this case. Ideal medium optimized conditions for maximuminhibition rate value: starch84.96g/L, soybean meal4.13g/L, K2HPO43H2O2.14g/L, MgSO47H2O1.23g/L, Glucose5/L, NaCl0.5g/L, and predicted value was72.03%. After experimental verification under the condition above, the inhibition rateis67.44%which is consistent with the theoretical predicted value, indicating that themodel is reasonable and effective. Maximum inhibitory activity increased of14.28%than the original medium. This study provides important theoretical and practicalbasises for further optimization of antifungal activity and high efficiency productionof antifungal substances produced byStreptomyces lydicus.