Engineering Strategies to Improve Cellulase Production: Trichoderma reesei as a Pellet

In this study, we demonstrate the use of surfactants and specific nutrient control to regulate the growth and behavior of Trichoderma reesei Rut C-30. Although T. reesei is the ubiquitous cellulase producing fungus, many practical engineering issues remain. Typical processing conditions utilize a high growth density complicated with high nutrient demand in a viscous filamentous biomass filled fluid phase. This work shows that surfactants can be used to alleviate these processing difficulties by leveraging the inherent cell biology to our advantage. Surfactants have long been used to reduce cellular agglomeration, lyse cells, and improve cellular membrane permeability. In fungal cultures the application the surfactants tends to produce variable, species dependent, responses. In the case of the normally filamentous T. reesei Rut C-30, certain surfactants were found to promote growth into a compact pellet formation (diameter 1 – 4 mm). These physical changes to the morphological structure have an overall positive effect on fermentation, allowing for improved mixing and mass transport through the continuous fluid phase. To improve yields and further decouple cellulase production from the growth phase, the restriction of key nutrients were tested. The specific control of phosphorus was found to successfully halt cell growth without affecting cellulase production. These results indicate that long-term cellulase can be continually produced from a pelleted, stationary phase, T. reesei culture.