Study of the Pgi deletion in Trichoderma reesei

T. reesei is widely used for industrial production of proteins. We have studied the role of pentose phosphate pathway (PPP) in T.reesei by deleting phosphoglucose isomerase (PGI) gene in the strain RutC30. This strain has also at least a partial inactivation in the glucose repressor gene cre1. Pgi mutants are unable to convert glucose-6P into fructose-6P and have the glycolysis blocked. PGI activity was absent in the knock-out mutants. The mutants showed morphological changes such as swolled, short and highly branched hyphae. Pgi mutants were able to grow in minimal medium (MM) with 1% glucose indicating that the PPP is active in Trichoderma in this mutant background. Cellulase activity was found to be higher in the pgi mutants on MM + 1% glucose in shake flasks than in RutC30, which did not produce cellulase activity. However, in a bioreactor on glucose, the maximum cellulase activity was 4-fold higher in RutC30 than in the pgi mutant. Endoglucanase 1 (egl1) mRNA was highly expressed during the exponential phase and at very low levels during the stationary phase in the RutC30 strain but was low in the mutant throughout the fermentation. Glucose consumption under this fermentation condition were 0.18 glu/h/g biomass and 0.0097 g gluc/h/g biomass for RutC30 and the pgi mutant, respectively. Cellulase activity produced per glucose consumed was higher in the mutant than in RutC30 (0.667 nkat/ml /g gluc and 0.129 nkatlml /g gluc, respectively).