Sunday, May 4, 2008
2-21

Fermentation Behaviors of Hypocrea jecorina RUT C-30 for Cellulase Production Using Lactose as Substrate

Chi-Ming Lo, Qin Zhang, and Lu-Kwang Ju. Chemical and Biomolecular Engineering, University of Akron, 200 E Buchtel commons, Akron, OH 44325-3906

Lactose is recognized as an inexpensive, soluble substrate that has reasonably good inducing capability for cellulase production by Hypocrea jecorina. The current knowledge suggests that the fungal species does not directly uptake lactose. Instead, lactose is hydrolyzed by extracellular enzymes, lactase and cellulase components, to glucose and galactose for subsequent microbial ingestion. The fermentation behaviors of H. jecorina grown on lactose have not been mechanistically investigated or modeled to consider this critical extracellular hydrolysis step. In this study, H. jecorina RUT C-30 was grown in both batch and continuous culture systems using lactose, lactose and glycerol mixture, glucose, galactose, as well as glucose and galactose mixtures as the substrate. The concentrations of sugar compounds and the activities of lactase and cellulase enzymes were measured along with the cell concentration. Glucose was found to repress the galactose consumption. The continuous culture results were used to calculate the lactose hydrolysis rate and the specific production rates of cellulase and lactase. The lactose hydrolysis rates were used to evaluate the kinetic contributions of lactase and cellulase to the hydrolysis. The specific production rates of cellulase and lactase were used to establish the effects of dilution rate and different sugar concentrations on the enzyme synthesis. A model was then developed to incorporate these relationships with the cell growth and substrate consumption kinetics to describe the overall fermentation behaviors. The experimental results were used in model fitting to generate a set of best-fit model parameters. The study provided significant conceptual and quantitative insights to the lactose metabolism and cellulase production by H. jecorina.

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