Fungi cellulase

For many years, plant cellulases were thought, contrarily to bacteria and fungi cellulases, not to have CBMs. Nevertheless, putative CBM sequences were found in a tomato cellulose, in 1998 [105]. Since then, putative CBMs were described in peach [106], pear [107], strawberry [108] and mango [109]. However, only recently the first CBM from plant was described (present in a tomato cellulase), and a new CBM family was born (CBM49) [110]. The tomato cellulase is highly sensitive to proteolysis in the linker region, when expressed in a heterologous system. Therefore, the respective sequence was fused with a catalytic domain of another well studied cellulase, from T. fusca. It was shown that the fusion enzyme was able to bind and hydrolyze crystalline cellulose. 

The second source of biochemicals is molecules excreted from cells such as extracellular enzymes and other organic matter. A typical example is cellulase, which is excreted by fungi such as Penicillium in order to break down wood and woody material into sugars that can be used by the organisms. Other common extracellular enzymes found in soil are ureases and amylases. Often enzymes are associated with clay particles, and in such associations, their activity may be increased, decreased, unchanged, or completely destroyed [15],... 

In the treatment of cellulose pulps one essential criterion for a suitable enzyme preparation is that its cellulase activity should be as low as possible, or preferably absent completely. As even extremely low cellulase activities may ruin pulp quality, Trichoderma enzyme preparations are unlikely to be suitable for these applications. Many bacterial and fungal enzymes with low cellulase activity have been shown to be suitable for treatment of pulps 14, 15, 16,17), Regulation of the often synchronous production of cellulolytic and hemicellulolytic enzymes in micro-organisms is not well understood, and is further complicated by substrate cross-specificity of these enzymes. Enzymes with both endoglucanase and xylanase activity have been reported for bacteria 18, 19) and fungi 20, 21, 22), In addition to selection of strain and... 

Comparison of Composition of Cellulase Systems of Various Fungi Produced in SSF... 

Cellulase-Negative Xylanase-Positive Mutants. There are two reports concerning the selection of such mutants from filamentous fungi, one on Pofyporus adm-tus (32) and the other cmi Trichoderma reesei (Durand, H. et al. Society CAYLA, Toulouse, France, unpublished results). An analysis of the eliminated cellulase genes has not been done, so it is not known if the mutants negative in endo(l- 4)-p-glucan-ase were deficient also in cellobiohydrolases. 

Xylanolytic systems of yeasts and fungi can also be induced by positional isomers of xylobiose. Induction with Xylp-p-(l- 2)-Xyl/7 is analogous to the sophorose induction of cellulase in filamentous fungi (76). Xylp-p-(l- 2)-Xyl/7 and Xylp-p-(l- 3)-Xyl/7 induced xylanase in C. albidus (77), Trichosporon cutaneum (73), A. pullulans (78) and A. terreus (Hrmova, M. et al., Slovak Academy of Sciences, Bratislava, submitted for publication, 1990). In C. albidus the positional isomers behave differently than does xylobiose (77), in that the response of the cells to them was slower but the enzyme yields were higher than in the presence of xylobiose. This in-icated that isomeric xylobioses were not direct inducers. In agreement with this idea, both Xylp-p-(l- 2)-Xylp and Xylp-p-(l- 3)-Xylp were transformed to Xyl/7-p-(l- 4)-Xyl/7, the natural inducer (79). 

It has been proposed that the production of xylanases and cellulases is under separate regulatory control in some filamentous fungi (1). Hrmova et al. (42) reached a similar conclusion after monitoring the daily production of these enzymes in Trichoderma reesei QM 9414. Xylanase and cellulase activities followed independent production profiles during fungal growth. The same effect has been observed in batch cultures of T. harzianum. We have observed peak xylanase activity on the third day of growth whereas the cellulase activity peaked after day five or six (unpublished). 

Table IV. Degradation of Cotton Cellulose by Cellulase Preparations from Three Cellulolytic Fungi in the Presence of Either Air, Nitrogen, or Oxygen ...

T. reesei, a saprophytic fungus, is capable of utilizing a variety of carbohydrates. Yet, only a few carbohydrates induce cellulase production. Inducers include cellulose, cellulose derivatives, lactose, and sophorose (31,32). Mandels and Reese (31,32) studied the inducibility of various sugars and found that sophorose is an excellent cellulase inducer in T. reesei while having little effect in other fungi or bacteria. On further examination they found that trace amounts of sophorose present in glucose caused the apparent ability of glucose to be a cellulase inducer in T. reesei. 

Cellobiose, a dimer of /3-1,4-linked glucose, is reported to be a cellulase inducer in T. reesei as well as in several other fungi (20,28,33, 34). But whether cellobiose is a true inducer is questionable since Reese et al. (35) reported that cellobiose could induce as well as inhibit cellulase biosynthesis. The same is also true for glucose. Whether glucose or cellobiose is an inducer or inhibitor depends on the concentration of sugars in the environment. 

T ine structural studies on woody cell walls attacked by ectoenzymes of fungi in situ are numerous (cf. 1,2). In contrast, investigations on the selective degradation of cell walls by enzymes isolated from fungi are few. Jutte and Wardrop (3) attempted the use of crude commercial cellu-lase preparations to determine the degradation pattern of Valonia cellulose and beechwood fibers. Similar use of commercial preparations of enzymes was made by Reis and Roland (4) to evaluate the nature of diverse cell walls and to show the distribution of polysaccharides. An endo-/ -l,4-xylanase with specific xylanolytic activities was isolated from a commercial cellulase preparation using chromatographic methods and... 

When cellulase activity is induced in higher plants, analysis shows it to be present in multiple forms, which differ in electrophoretic and/or chromatographic mobility (3,13,15-18). These forms are analogous to those found in fungi in at least one respect, namely, that they include two or more endohydrolases which can attack CMC (CMCases). There is only one report of a plant exocellulase (16) and none of the synergistic... 

Ci activity (1,2), but / -glucosidase and cellobiase activities are probably ubiquitous (e.g., see Ref. 14 and 16). Whether or not these together constitute a cellulase complex as in fungi is unknown. The possibility seems unlikely since there are so few occasions in plants when whole cellulose microfibrils are autolyzed, and there is no need for it on nutritional grounds. Nevertheless, the question remains of why specific plant cells or tissues often elaborate more than one endocellulase. 

Many fungi are capable of producing extracellular enzymes that can degrade cellulose. They are Trichoderma (T) reesei, T. viride, T. koningii, T. lignorum, Penicillium funiculosum, Fusarium solani, Sclerotium rolfsii, and so on. Bacterial species such as Cellulomonas along with Clostridium thermocellum can also produce cellulases (Marsden and Gray, 1986). 

Trichoderma reesei RUT C30 is known to be one of the best hyperpro-ducing cellulolytic fungi. Several factors, such as the amount and quality of carbon source, temperature and pH of the cultivation, and aeration, influence enzyme production of this strain. It has been indicated in previous studies that pH and the pH-controlling strategy have a great effect on the amount of cellulase produced (1-9). 

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