At the industrial scale, enzymes are produced by the fungus Trichoderma reesei. Under inducing conditions, it secretes large amounts of cellulases and hemicellulases. In most cases, lactose is used as the inducer, as it efficiently and strongly induces cellulase and, to a minor extent, hemicellulase expression. However, it represents a relatively costly substrate and substituting it could be an option to reduce global enzyme production costs.
In this context, the use of cheaper and readily available sugars as global inducers is a tempting alternative. The liquid hydrolysate obtained after steam explosion pretreatment contains mono- and oligosaccharides including C5 sugars which could be used to induce cellulose gene expression. Moreover, these sugars could also induce hemicellulase genes more efficiently than lactose.
In this study, we selected several motifs in the promoting sequences of the main hemicellulases encoding genes that have been described to be responsible for their induction by C5 sugars. To evaluate the possibility of these motifs to mediate induction by hydrolysates when transferred to other promoters, we integrated them into the promoting sequence of a reporter gene. Five different constructs have been designed and the change of the inducibility of the resulting promoter was measured. Expression analyses show that the induction profile of the reporter gene can be changed as a result of promoter engineering.