Recombinant enzymes from thermophilic micro-organisms expressed in fungal hosts

Abstract

Cost-effective production of enzymes for industrial processes makes the appropriate selection of the host/vector expression system critical. We have tested two fungal systems for the bulk production of enzymes from thermophiles. The yeast Kluyveromyces lactis has been developed as a secretion host employing expression vectors based on the 2u-like plasmid pKD1 of Kluyveromyces drosophilarium. Our second system involves the filamentous fungus Trichoderma reesei. Signal and protein fusion vectors have been constructed using the strong cellobiohydrolase 1 (cbh1) promoter and recombinant plasmid DNAs introduced into various high-secreting T. reesei strains using biolistic particle delivery. In some cases (e.g. the xynB gene of Dictyoglomus thermophilum) we have reconstructed the genes according to Trichoderma codon preferences and demonstrated a dramatic increase in the production of the enzymes. The heterologous XynB enzyme is glycosylated differently in different Trichoderma strains. A proteomics approach has been taken to identify strongly expressed proteins produced by T. reesei under various cultivation conditions in order to identify condition-specific promoters driving the production of these proteins. Analyses indicated that HEX1, the major protein of the fungal Woronin body, is a dominant protein under both cellulase-inducing and -repressing conditions. The hex1 gene together with its promoter and terminator sequences has been isolated and the promoter function studied relative to cultivation time and medium.