Fungal cellulases

#The present invention relates to novel enzymes. More specifically, the invention relates to novel fungal cellulases and methods of obtaining the DNA encoding them.

#There is an increasing interest in glucanases in the food and feed industries. These enzymes find application for instance in the fruit juice industry for liquefaction of plant cell wall material (pending application EP 94202442.3). They may also serve as processing aids to reduce fouling of membranes. In the feed industry the role of β-glucanases in reducing the viscosity of various sorts of grains is well established. Many of the enzyme preparations used in the food and feed area are derived from Aspergillus species, usually Aspergillus niger. This is a safe host which produces a large variety of enzymes such as pectinases and hemicellulases with characteristics which make them suitable for applications at moderate temperatures and at neutral to acidic pH. In contrast to pectinases and hemicellulases, cellulases are usually derived from Trichoderma. Trichoderma species such as reesei, viride or longibrachiatum are good producers of cellulolytic enzymes. However, Trichoderma enzymes cannot be used everywhere due to regulatory constraints. Thus, it would be of considerable economic value to have a good source of Aspergillus enzymes. However, up till now, it has not been possible to clone the genes encoding glucanases from A. niger using the traditional method involving enzyme purification, partial amino acid sequencing and isolation of the gene or cDNA for the enzyme of interest by the derived DNA sequence.

#The present invention provides polypeptides with cellulase activity, corresponding DNA sequences, vectors, transformed hosts and a method for the production of these polypeptides which are obtainable from Aspergillus niger var. niger or Aspergillus niger var. tubigensis.

#FIG. 1 shows viscosity reduction due to CMCase activity of Aspergillus niger cellulases.

#FIG. 2 shows viscosity reduction due to β-glucanase activity of Aspergillus niger cellulases.

#The present invention relates to novel fungal cellulases and to methods of identifying the DNA which encodes these fungal cellulases.

#In the method according to the invention, fungal cellulases are cloned by expression cloning using a cDNA library in the form of prokaryotic host cells which have been transformed with DNA which is obtainable from fungi. Screening of the host cells is performed after the cDNA has been inserted into a plasmid. The prokaryotic host cells are preferably bacterial cells, more preferably E. coli.

#In the present context, the term ‘cellulase’ refers to an enzyme which degrades carboxymethyl cellulose (CMC) and/or β-1,3-glucan and/or β-1,4 glycan and/or xyloglucan.