Characterization of growth and sporulation of Metarhizium anisopliae in solid-substrate fermentation

The entomopathogenic fungus Metarhizium anisopliae was cultivated by solid-substrate fermentation both with and without forced aeration using a medium based on a mixture of rice bran and rice husk: the water activity was fixed at an initial value of 0.998. An equation to describe the growth and sporulation processes was derived from stoichiometric considerations. By means of elemental mass balances and using the concept of c-mole, the stoichiometric coefficients of the growth equation were determined. It was concluded that under the culture conditions tested, M. anisopliae can grow at a maximum specific growth rate of 0.08 h(-1). After 90-100 h of culture when growth has stopped a spore yield of 2.3 x 10(10) spores g(-1) rice bran was obtained. This is as high as 80.4% of the maximum theoretical value. The heat generated during the culture did not affect growth and sporulation since even when high initial amounts of solids were used, no desiccation was observed. Nevertheless, the yields obtained under these conditions suggested the appearance of another type of growth limitation not related to substrate consumption.