Monday, May 4, 2009
5-11
Effect of the carbon source consumption rate on cellulase production by Trichoderma reesei in fed-batch cultures
One of the most effective industrial micro-organism used for the production of the cellulolytic enzyme cocktail suitable for the hydrolysis of ligno-cellulosic biomass is the imperfect fungus Trichoderma reesei, mainly thanks to its high secretion capacity. One option to decrease the cellulase production cost is increasing the cellulase secretion productivity which is a function of cell density and specific production rate. From a process optimisation standpoint, maximizing this rate requires understanding the dynamics of growth, substrate consumption and enzyme production. The organism ability to grow and produce enzymes is affected by the nature of the carbon source used and by its specific consumption rate. The relationship between the carbon source and the regulation of the cellulase genes in T. reesei is already partially characterized but data on specific production rates and activity of the proteins at different physiological states of the cells are scarce. For this purpose, we have investigated the kinetics of growth and cellulase production, in carbon-limited cultures at various specific consumption rates. In the present study, T. reesei was cultivated in a bioreactor using a fed-batch mode in order to be in perfectly controlled cultivation conditions, similar to industrial ones. Carbon, nitrogen and redox degree balances were calculated all through the fermentation in order to determine the specific rates, yields, cellulolytic activities and the main parameters likely to affect the cellulase production rate.
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