Study On Kinetics Of Liquid Fermentation In Metarrhizium Anisopliae IMI330189

Metarhizium anisopliae strain IMI330189is of high efficiency in locust control and has been usedin locust control in South Africa and China’s grassland. In this paper, the fermentation medium and theliquid fermentation conditions of Metarhizium anisopliae strain IMI330189were optimized, and theliquid fermentation kinetics were studied. The results are as follows:Under the condition of liquid volume200mL/1000mL flask,200r/min,27°C, the optimized shakeflask fermentation conditions are as follows: the fermentation time of seed is72h, fermentation time is85h, the initial pH is6~6.5, and the inoculum is2.5%.Liquid fermentation medium for189strain was optimized by response surface method (RSM).Firstly, three factors which have a significant impact on the biomass had been screened out from sixmedium composition by the use of Plackett-Burman design: sugar, yeast extract and FeCl36H2O;secondly, the response region of central composite design was determined by the steepest ascent test;Finally, the optimal concentration of the three significant factors were determined by the use of centralcomposite design and response surface analysis. The optimized medium composition is: sucrose44.394g/L, yeast extract17.104g/L, FeCl3·6H2O0.206g/L, K2HPO46g/L, MgSO4·7H2O1.5g/L, andCaCl20.4g/L, respectively. In the optimized medium, the biomass of Metarhizium anisopliae reached25.028g/L,63%higher than that in the initial medium.Kinetic models of biomass growth, suger consumption and nitrogen consumption were established,and the parameters of the models were determined by Origin7.5software. The results showed that themodel simulation matched well with the experimental observations, the fitted models basically reflectthe liquid fermentation process of189strain. The change of specific rate during the fermentation processwas analyzed. The maximum specific growth rate was found to be0.084h-1at22.8h, specific total sugarconsumption rate0.246h-1at9.6h and specific total nitrogen consumption rate0.007h-1at10.3h. Themaximum yield coefficient of biomass from total sugar was0.861g/g at39.8h.Finally, the Metarhizium anisopliae was cultivated using the optimized liquid fermentation medium,then the solid fermentation carrier were inoculated with the broth in different fermentation age for solidfermentation, linked liquid fermentation and solid fermentation of Metarhizium anisopliae. Therelationship between solid state fermentation sporulation and the state of fermentation broth at the end ofliquid fermentation was analyzed, and draw the conclution that the following parameters should beconsidered to deside the end of liquid fermentation: culture time51~75h; cell in the middle and lateperiod of exponential growth and the biomass have reach15~20g/L; the fermentation broth is lightbrown and sticky; pH value is about5and stable and has not start to rise.