Fungi, cellulolytic enzymes

Many microorganisms, particularly fungi and thermophilic bacteria, possess cellulolytic enzymes of different kinds (10-21). Because of their... 

The filamentous fungi investigated showed coinduction of cellulolytic and xylanolytic enzymes. During growth on cellulose, products from the hydrolysis of cellulose also induced production of xylanolytic enzymes, and during growth on xylan, products from the hydrolysis of xylan also induced the production of cellulolytic enzymes. 

Most bacteria are incapable of degrading crystalline cellulose since their cellulase systems are incomplete. However, the cellulolytic enzymes produced by some fungi generally involve all three types of enzymes, so they are very useful in the saccharification of renewable cellulosic resources. 

Cellulose-hydrolyzing enzymes are widespread in Fungi and Bacteria. Less thermoactive cellulases have already found various biotechnological applications. The most effective enzyme of commercial interest is the cellulase produced by Tricho-derma sp.[661. Cellulolytic enzymes can be used in alcohol production to improve juice yields and effective color extraction of juices. The presence of cellulases in... 

These factors are largely self-explanatory. Low-molecular fragments are more accessible to microbial systems of fungi (which are often secreted by fungi and have to diffuse into the matrix they are attached to). The higher the temperature, the more active the enzymes, unless the temperature is too high (temperature maximum for their activity is often between 40 and 45°. C, that is, 100-110°F). Cellulolytic enzymes have pH optimum for their activity between 4 and 6, that is, in a slightly acidic area. 

The cellulolytic enzymes of fungi are mostly present in the liquid in which the organism has been grown. The fungus is normally cultured in a liquid medium containing cellulose and different mineral salts. The culturing process is followed by filtration or centrifugation to remove the cells and residual cellulose. 

Figure 12. Logarithmic plot of the molecular radius of the equivalent hydrodynamic sphere against molecular weight for cellulose of Myrothecium verrucaria (77) and other globular proteins. This relationship was used to estimate the probable size of cellulolytic enzymes of other fungi as shown in Table V...

Figure 1. Hydrolysis of cotton by organisms and by cell-free enzymes (17). Growth tests—Consumption of cellulose by active cellulolytic fungi. Trichoderma enzyme— - weight loss of cellulose). Other enzymes—Cell-free celluloses from organisms other than Trichoderma...

Cellulolytic enzymes are common in marine lignicolous fungi [6,7]. Around 25% of the 40 species tested by Rohrmann [20] showed the same cellulase activity as Sporotrichum pulverulentum, a strongly cellulolytic terrestrial deuteromycotina. In salt-marsh species, enzymatic activity against carboxymethylcellulose was found in 100% of the 19 species... 

As referred previously, two main types of cellulolytic systems are currently recognized. Those based on free , soluble enzymes, produced mostly by aerobic microbes that secrete individual cellulases, which act synergistically on native cellulose and those based on complexes of cellulolytic enzymes, or cellulosomes , produced by some anaerobic bacteria and fungi, which are usually attached to the outer surface of the microorganism [40, 101]. CBMs play a role in the phase transfer of a soluble free enzyme onto the insoluble substrate [68, 69]. CBMs are present in several polysaccharide-degrading enzymes, namely in hemicellulases [56, 58, 102], endomannanases [12], xylanases [56, 103], acetyl-xylanesterases [104] and )3-glucosidases [71]. 

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... 

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). 

Teunissen MJ, Smits AA, Op den Camp HJ, Huis in t Veld JH, Vogels GD (1991) Fermentation of cellulose and production of cellulolytic and xylanolytic enzymes by anaerobic fungi from ruminant and non-ruminant herbivores. Arch Microbiol 156 290-296 Tielens AG, Rotte C, van Hellemond JJ, Martin W (2002) Mitochondria as we don t know them. Trends Biochem Sci 27 564-572... 

The cellulolytic system of soft-rot fungi has received relatively little attention. It is probably similar to that of the closely related Ascomycetes and Fungi Imperfecti 19-25, 27), which apparently differs little from that of white-rot fungi, except perhaps in the absence of oxidizing enzymes. 

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