Biomass which largely consists of cellulose, hemicellulose and lignin has attracted increasing attention as an important renewable source of energy (including nutritional energy). The amount of carbon fixed by photosynthesis has been estimated to be 100.times.10.sup.9 tons per year worldwide, and half of that is contained in cellulose. If this material, or at least a significant part of it, could be converted into liquid fuel, gas and feed protein, this would constitute a significant contribution to solving the problem of recycling and conservation of resources. However, it has been found difficult to develop an economically viable process of converting cellulosic material into fermentable sugars.
The currently most promising of the suggested processes involves the use of enzymes which are able to degrade cellulose. These enzymes which are collectively known as cellulases are produced by a number of microorganisms, including fungi (e.g. Trichoderma reseei, Humicola insolens, Fusarium oxysporum, etc.) and bacteria (e.g. Clostridium thermocellum, Cellulomonas spp., Thermonospora spp., Bacterioides spp., Microbispora bispora, etc.). The economics of the production of fermentable sugars from biomass by means of such enzymes is not yet competitive with, for instance, the production of glucose from starch by means of .alpha.-amylase due to the ineffeciency of the cellulase enzymes. The most significant problems connected with the use of cellulases is their low specific activity and the high cost of their production. Therefore, there is a need to develop cellulases which are more efficient in degrading cellulosic materials into fermentable sugars.
Apart from their utility for the degradation of biomass, cellulases have also been suggested for use in detergent compositions for the treatment of cotton-containing fabrics which largely consist of cellulose. It is well known that repeated washing of cotton-containing fabrics generally causes a pronounced, unpleasant harshness in the fabric due to the presence of amorphous regions in the cellulose fibres, which regions form protruding parts on the otherwise smooth fibres. Several methods for overcoming this problem have previously been suggested. For example, U.S. Pat. No. 1,368,599 of Unilever Ltd. teaches the use of cellulases for reducing the harshness of cotton-containing fabrics. Also, U.S. Pat. No. 4,435,307 (of Novo Industri A/S) teaches the use of a cellulytic enzyme derived from Humicola insolens as well as a fraction thereof as a harshness reducing detergent additive. Other uses of cellulases mentioned in the art include soil removal frown and colour clarification of fabric (cf. for instance EP 220 016).
Although the use of cellulase enzymes for harshness reduction of cotton-containing fabrics was suggested and demonstrated nearly 20 years ago the mechanism of this process has not been elucidated and is still not known in detail. Among other things, this is due to the multiplicity of the enzymes and the enzyme-catalyzed reactions involved. As a matter of fact, cellulases generated in nature e.g. by microbial species are indeed complex mixtures of cellulases. Accordingly, the conversion of naturally occurring materials, like cotton, catalyzed by cellulases is exceedingly difficult to analyze in detail.
Due to these circumstances, the practical exploitation of cellulases for harshness reduction and prevention as well as colour clarification, however desirable, has not become widespread and of great practical utility: it is difficult to optimize production of multiple enzyme systems and thus to implement industrial cost-effective production of cellulase enzymes, and their actual use has been hampered by difficulties arising from the need to employ rather large quantities of the cellulases to achieve the desired reduction and prevention of the harshness of cotton fabrics: for instance, addition of large quantities of the enzymes to detergent compositions is not compatible with the optimal function of other ingredients in the detergent formulation nor is the addition of very large quantities of enzymes to the detergent composition in the interests of, e.g., consumer safety.
The object of the present invention is therefore to provide cellulase enzymes with a high specific activity.