[Optimization of the medium and fermentation condition for the Z12 strain with molluscicidal actions against ].

OBJECTIVE

To optimize the culture and fermentation conditions of the Z12 strain, a fungal strain with molluscicidal actions against , so as to provide the basis for the research and development of molluscicidal active substances from the Z12 strain and its fermentation broth and large-scale fermentation.

METHODS

The carbon source, nitrogen source and mineral salts were identified in the optimal culture medium for the Z12 strain with a single-factor experiment to determine the best fermentation condition for the Z12 strain. Factors that significantly affected the growth of the Z12 strain were identified using the Plackett-Burman design, and the best range of each factor was determined using the steepest climb test. Response surface analyses of temperature, pH value, seeding amount and liquid-filling quantity were performed using the Box-Behnken design to create a regression model for fermentation of the Z12 strain to identify the optimal culture medium.

RESULTS

Single-factor experiment preliminarily identified the best culture medium and conditions for the Z12 strain as follows: sucrose as the carbon source at approximately 20 g/L, tryptone as the nitrogen source at approximately 5 g/L, KHPO as the mineral salt at approximately 5 g/L, initial pH at approximately 8, temperature at approximately 28 °C, seeding amount at approximately 6%, and liquid-filling quantity at approximately 50 mL/100 mL. Plackett-Burman design showed that factors that significantly affected the growth of the Z12 strain included temperature ( = -5.28, < 0.05), seeding amount ( = 5.22, < 0.05), pH ( = -4.30, < 0.05) and liquid-filling quantity ( = -4.39, < 0.05). Steepest climb test showed the highest mycelial growth at pH of 7.5, seeding amount of 8%, and liquid-filling quantity of 40 mL/100 mL, and this condition was selected as the central point of response surface analysis for the subsequent optimization of fermentation conditions. Response surface analyses using the Box-Behnken design showed that the optimal conditions for fermentation of the Z12 strain included sucrose at 15 g/L, tryptone at 5 g/L, KHPO at 5 g/L, temperature at 28.2 °C, pH at 7.5, seeding amount at 10%, and liquid-filling quantity at 35.8 mL/100.0 mL, resulting in 0.132 g yield of the Z12 strain.

CONCLUSIONS

The optimal culture condition for the Z12 strain has been identified, and the optimized culture medium and fermentation condition may effectively improve the fermentation yield of the Z12 strain.