Rumen cellulase

RunUnococcus albus and Ruminococcus flavefadens. These bacteria are important cellulose-degraders found in the rumen of cattle and sheep (2). Most isolated strains ferment cellulose and xylan and all ferment cellobiose. Fermentation of glucose and some other carbohydrates depends on the particular strain. R flavefadens and B. succinogenes can ferment the highly ordered crystalline cellulosic su trates but R albus cannot. No evidence has been found for extracellular cellulase production by R albus, but Ohmiya et al. purified cellobiosidase from this culture 17). Laboratory growth of R albus has been conducted at pH 7.0 and 37 C. 

The biodegradation of cellulose is caused by enzymes known as cellulases [471-475]. Cellu-lases are produced by many microorganisms (bacteria and fungi). The most widely studied cellulases are of fungal origin, e.g., Trichoderma [471,473]. The cellulose-digesting bacteria of the rumen are a complex anaerobic community [476,477]. 

Although fungal cellulases are often more active, bacteria, particularly those of the rumen, have high cellulolytic activity (28). Hungate recently reported (29) that the cellulase of Ruminococcus album is partially inhibited by oxygen. This may account for the difficulty in isolating active cellulases from rumen organisms. 

White BA, Cann IKO, Mackie RI, Morrison M (1997) Cellulase and xylanase genes from ruminal bacteria domain analysis suggests a non-cellulosome-like model for organization of the cellulase complex. In Onodera R, Itabashi H, Ushida K, Yano H,Sasaki Y (eds) Rumen microbes and digestive physiology in ruminants. Jpn Sci Soc Press, Tokyo, p 69... 

Using mixed bacterial preparations isolated from the rumen, King (18) offered the evidence for the presence of surface-localized cellulase... 

Pew (26) found digestibility of hardwoods by cellulases improved markedly by pretreatment with aqueous NaOH the effect was considerably more pronounced with hardwoods than with softwoods. Stranks (35) reported that the in vitro rate of digestion of hardwoods by rumen-inhabiting bacteria, measured by succinic acid production, was markedly increased by pretreatment with 1-5% NaOH, whereas softwoods were unaffected by the treatment. The effect of NaOH in improving the digestibility of straw has long been known (5). 

Although cellulase activity of rumen microflora is high, lignocellulose feed stuffs are only partially degraded that is, only part of the potential energy is made available for animal production. 

Under the conditions of the assay employed, cellulase activity could not be detected in the supernatant fluid (enzyme fraction 3) of rumen contents. Enzyme fraction 2 which was obtained by ultrasonic disruption of cells in the liquid portion of rumen contents exhibited appreciable activity on CMC but not on Avicel or Solka Floe. On the other hand,... 

Table VIII. Distribution of Cellulase Activity in Rumen Contents...

A new procedure described for the determination of cellulase activity is based on incubation of the enzyme with finely divided cellulose at pH 6.9 and determination of the D-glucose and cellobiose liberated as their trimethylsilyl derivatives by g.l.c. The method, although generally applicable, was specifically developed for measurement of cellulase activity in mixed enzyme preparations from sheep rumen contents the coefficient of variation of the assay was 2.4-4.5%. 

Fig. 10.1 Laboratory methods for estimating the dry matter digestibility of forages, (a) Incubation in rumen liquor followed by digestion with pepsin, (b) Digestion with pepsin followed by digestion with cellulase.

Cellulases play an important role in the natural decomposition of plant residues and are produced by cyllolitic microorganisms including aerobic saprophytes, anearobic rumen bacteria and anearobic thermophilis spore formers. Similar to amylases, the cellulases operate in Uvo modes endo or exo-cellulase. 

Factors affecting the cellulolytic activity of rumen contents have been examined. The levels and nature of cellulase activity during growth of Achlya bisexualis on D-glucose, cellulose, and selected polysaccharides have been studied. ... 

Studies on the adaptive nature of the cellulolytic enzyme from Chaetomium aureum have shown that cellulase is induced only in media supplemented with cellulose. Multiple cellulases produced by a soft-rot bacterium (Erwinia carotovora) have been investigated, and some fractionation of these enzymes was achieved. A cellulolytic bacterium (Micromonospora ruminantium sp. novo) has been found in sheep rumen. ... 

Yucca schidigera and Quillaja saponaria containing 4.4% and 10% saponins (Wang et al. 1998) decreased polysaccharide degrading enzymes (carboxymethyl-cellulase and xylanase) considerably and inhibited protozoa to the extent of 42% and 54% respectively (Hristov et al. 1999, 2003). Wang et al. (1998) studied the effect of yucca extract (0.5 mg/ml buffer) on rumen fermentation in RUSITEC and reported no effect on dry matter digestibility, gas production and volatile fatty acid production, but the protozoa numbers were significantly reduced, while the number of bacteria was not affected. 

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