Abstract
Acetic acid is one of the major potential inhibitors of cellular growth resulting from acid pretreatment of lignocellulosic biomass. To use lignocellulose hydrolysate in biorefineries it is necessary to assess their effect on the microorganisms likely to be used. An attractive option is to use a part of these hydrolysates for on-site cellulase production. Based on an industrial process that included a fast initial growth phase, the effect on Trichoderma reesei grown on glucose was assessed and modeled at different concentrations and pH. Acetic acid had a strong effect on T. reesei growth rate and yield, which correlated only with the concentration of the undissociated form in solution. The specific growth rate was accurately modeled by two different classic inhibition models as a function of pH and total acetic acid concentration. Co-consumption of glucose and acetic acid was observed, so that the culture medium was gradually detoxified by the cells. With or without glucose, acetic acid was mineralized into carbon dioxide at a similar specific rate, but no growth was observed without glucose. A 2.5-fold increase in the maintenance coefficient was observed, due to the need for glucose consumption to preserve cell integrity, which corresponded to a one-third decrease in the overall biomass yield. The resulting models can be used to simulate T. reesei growth on acetic acid-containing media and to choose the optimum pH for efficient growth on lignocellulosic biomass hydrolysates.
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