Multiplicity and expression of xylanases in the rumen fungus Neocallimastix frontalis

The time course production of xylanolytic enzymes by the rumen anaerobic fungus Neocallimastix frontalis was studied during growth on different carbon sources and revealed using isoelectric focusing and immunoblotting. A constant low level of endoxylanase expression was observed in glucose medium. A high level of xylanase activity was detected in methyl glucoside medium corresponding to the induction of new isoforms which were repressed by the presence of glucose. beta-Xylosidases were constitutively produced at a high level and remained mainly associated to the fungal cells. Polyclonal antibodies raised against the endoxylanases XYLI and XYLII revealed that XYLI was secreted to the different culture media showing a characteristic pattern of constitutive expression, while anti-XYLII recognized several polypeptides larger than XYLII indicating the production of multiple antigenically related enzymes during growth on the inducing substrate.