Sophorolipids-induced cellulase production in cocultures of Hypocrea jecorina Rut C30 and Candida bombicola

Sophorose is a potent but expensive inducer for cellulase production. In this study the feasibility of using sophorolipids, natural lipids that contain sophorose, for cellulase induction was investigated. Enhanced cellulase production by Hypocrea jecorina Rut C30 grown on glycerol, a substrate without cellulase-inducing ability, was first confirmed by addition of the crude sophorolipids collected from Candida bombicola fermentation. Cocultures of H. jecorina Rut C30 and C. bombicola were then employed to evaluate the effects of coculture conditions: the cell concentration ratio between the two cultures, the concentration of vegetable oil (as lipid precursor for sophorolipid synthesis, in addition to glycerol as the primary carbon source), the presence of nitrogen source for growth, and the substitution of glucose for glycerol as the primary carbon source. Specific cellulase productivity of H. jecorina Rut C30 was significantly higher under the conditions that promoted sophorolipid production by C. bombicola. The ability of H. jecorina Rut C30 to degrade sophorolipids was also confirmed. The results of the study indicated that the sophorolipids produced by C. bombicola can be degraded by H. jecorina Rut C30 and the sophorose generated from the degradation can effectively induce the fungal cellulase synthesis.