Fungus-Yeast Tri-culture System for In Situ Cellulase Production, Biodetoxification, and Bioethanol Production Using Rice Straw with Cyclic Shifting of Temperature Strategy

Abstract

The current study employs a tri-culture system, involving Trichoderma reesei and Penicillium janthinellum for cellulase production followed by the utilization of Saccharomyces cerevisiae for bioethanol production using pretreated rice straw as substrate. The fungal co-culture resulted in the production of maximum cellulase enzyme with the following activities: FPase, 1.09 IU/mL; CMCase, 24.47 IU/mL; beta-glucosidase, 4.74 IU/mL; and xylanase, 36.74 IU/mL respectively. Furthermore, the current work also represents a lesser studied aspect, concomitant biodetoxification, and cellulase production. Both T. reesei and P. janthinellum were able to metabolize the acid pretreatment by-products such as formic acid, acetic acid, HMF, and furfural. By implementing a cyclic shifting of temperature strategy, a maximum bioethanol titer of 17.05 g/L with a productivity of 0.405 g/(L × h) was achieved using the tri-culture system. This represents a 3.7-fold improvement compared to the SSF process conducted at the mutual optimum incubation temperature of 37 °C. This study presents a scope for a one-step process for fungal cellulase production and biodetoxification of the lignocellulose pretreated hydrolysate to avail an inhibitor-free medium for subsequent yeast co-culture for bioethanol production.