Systemic analysis of lactose metabolism in Trichoderma reesei identifies a lactose permease that is essential for cellulase induction. Trichoderma reesei

Lactose (1,4-0-ß-d-galactopyranosyl-d-glucose), a by-product from cheese manufacture or whey processing industries, is known to induce the formation of plant biomass hydrolyzing enzymes needed for the biorefinery industry in the fungus Trichoderma reesei, but the reason for this induction and the underlying mechanism are not fully understood. Here, we used systems analysis of the Trichoderma reesei transcriptome during utilization of lactose. We found that the respective CAZome encoded glycosyl hydrolases specifically tailored for the attack of monocotyledon xyloglucan. In addition, genes for a high number of putative transporters of the major facilitator superfamily were also induced. Systematic knock out of them identified a gene whose knock-out completely impaired lactose utilization and cellulase induction in Trichoderma reesei. These data shed new light on the mechanism by which Trichoderma reesei metabolizes lactose and illuminate the key role of ß-D-galactosides in habitat specificity of this fungus. Overall design: We used two biological replicas of Trichoderma reesei growing on lactose, glucose and glycerol