Cellulase synthesis

Bacteria represent a promising source for the production of industrial enzymes. Bacterial cellulases are an especialfy interesting case in point. Many thermophilic bacterial species produce cellulases that are stable and active at high temperature, resistant to proteolytic attack, and stable to mechanical and chemical denaturation. However, cellulase productivities in bacteria are notoriously low compared to other microbial sources. In this paper bacterial enzyme production systems will be discussed with a focus on comparisons of the productivities of known bacterial cellulase producers. In an attempt to draw conclusions concerning the regulation of cellulase synthesis in bacterial systems, a tentative model for regulation in Acidothennus cellulofyticus has been developed. 

The third group is that of compounds which may potentially be transported by the PTS and inhibit cAMP production. Cellulase synthesis is initiated after these compounds are consumed for cell growth. This group includes D-glucose, D-fructose, maltose, mannitol, glycerol, sorbitol, and -methyl glucoside. The presence of these compounds in Solka Floe fermentations, enhanced enzyme yields (132 to 254%) but the time required to complete cellulase synthesis took longer (106 to 148%) than the control. 

Acidothermus cellulolyticus cellulase activity, 334,335/,341,342/ cellulase production parameters, 341,343r cellulase synthesis regulation, model development, 341-346 concentration vs. rate of cellulase synthesis, 344,345/... 

Table I. Biochemical Mechanisms Controlling Cellulase Synthesis and Activity in Trichoderma reesei...

All naturally occurring fungal strains of Trichoderma require an inducer for cellulase synthesis. In the absence of an inducer such as cellulose, cellobiose (21,22), or sophorose (12,13,14,23), Trichoderma does not make any detectable cellulase complex enzymes. The true physiological inducer of cellulase is currently unknown. Insoluble cellulose is presumably not such an inducer since there is no way for the internal cell machinery to sense the presence of this insoluble material. However, a small transglycosylation product such as sophorose, 2-0-/ -glucopyranosyl-D-glucose, may well be the natural inducer. 

Pseudomonas fluorescens produced two extracellular (A and B) and one cell-bound (C) cellulase components, the latter being released by treatment with EDTA-lysozyme in isotonic sucrose. Culture with 0.5% glucose formed little cellulase. Cellobiose stimulated only the synthesis of C. The formation of A and B was strikingly enhanced in cultures with cellulose, sophorose, or continuous low concentration of cellobiose. The absence of extracellular cellulase synthesis in 0.5% cellobiose culture may be caused by catabolite repression. The three cellulases were purified and characterized. None of them split cellobiose, but all hydrolyzed various cellodextrins and celluloses. C easily attacked cellotriose and cellotriosyl sorbitol, but A and B had no effect. When pure B was incubated with broken spheroplasts of sophorose-grown cells, a cellulase component indistinguishable from A was formed. 

Since the inhibition of cellulase synthesis in 0.5% cellobiose culture seems to be caused by so-called catabolite repression as reported for the formation of many other hydrolases, the same results would be expected for other metabolizable sugars, which will show an enhanced cellulase synthesis depending on the supply conditions. Most of the sugars tested... 

As shown in Table VI, only slight changes in the relative CMCase activity were found in the mixtures of the cellulase components A and C with any of the broken spheroplast preparations, while a considerable increase in the activity was noticed in the mixtures with the component B. The enhancement in the mixtures treated with those SI and S3 was particularly high, which were both the broken spheroplasts from the cultures of an exo-type cellulase synthesis the cellulase activity was enhanced five times that of the original. S2 preparation from the culture of an endo-type cellulase synthesis was much lower in the activating... 

T t has been reported that fungal cellulases are induced enzymes and that cellulose preparations induce cellulolytic activity while easily assimilable carbon sources give the best fungal growth but less production of enzyme activity (9,12, 14). For example, Horton and Keen (10) found that 7.5 X 10"3M D-glucose repressed the synthesis of cellulase to a basal level in Pyrenochaeta terrestris and suggested that cellulase synthesis was regulated by an induction-repression mechanism. 

A 10% wheat bran suspension in water was autoclaved for 30 min at 115 °C and the resulting soluble (liquor) and insoluble components (residue) were separated by filtration. The liquor and residue fiactions were then used alone or mixed with 1 % MCC as carbon sources for P. decumbens growth. The biomass in cultures grown on wheat-bran liquor plus MCC was less than that on wheat-bran residues plus MCC, but the cellulase activity released was higher (Fig. 4). The liquor apparently contained a factor that stimulated cellulase synthesis and/or secretion. In contrast, the xylanase activity in the supernatants of cultures supplemented with wheat-bran liquor was lower than that in cultures supplemented with the wheat-bian residues, which were in consistent with the residues having higher hemicellulose content. 

Our original focus was on auxins and how they elicit growth in intact plants. Accordingly, we employed a semi-intact pea epicotyl system in which the plumule and hook were cut off to remove meristematic cells and the major supply of endogenous auxin, and the cut stump was painted with lanolin containing various additives. Our earlier findings with this system showing that auxin induces cellulase synthesis in vivo and in vitro have been reported [12]. 

Eveleigh, and B. S. Montenecourt, Increased endoplasmic reticulum content of a mutant of Trichoderma reesel (Rut-C30) in relation to cellulase synthesis. Enzyme Microb. Technol., 4 110 (1982). 

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