Cellulase inducer, cellobiose

While cellobiose is a poor inducer, lactose, the milk sugar, is a good inducer of cellulase biosynthesis. Lactose-induced fungus produces a cellulase complex which is identical to those cellulases induced by cellulose (for SDS gels see Figure 9b, e, h, i). 

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. 

Langsford et al. reported that Cellulomonas fimi culture supernatants contained cellulase and proteinase activities, for which there appeared to be a relationship. Glucose repressed the synthesis of both activities and cellulose induced both 60), Adding cellulose to Cellulomonas sp. (NRCC 2406) cultures stimulated growth and improved production of cellulases 61). Optimum conditions for growth and cellulase production were pH 6.5 and 30 C. The addition of glucose in the presence of cellulose inhibited growth. Several species of Cellulomonas have cellobiose phosphorylase. 

The stimulation of the synthesis of the cellulase system of T. reesei QM 9414 by sophorose was established as shown by the results of experiments summarized in Table IV. Other than sophorose, of the glycosides and oligosaccharides tested, only lactose caused even a limited production of the enzymes of the cellulase system. Lactose is not as closely related structurally to sophorose as is, for example, the disaccharide laminaribiose it is more closely related structurally to cellobiose, which, despite being the major product of cellulose breakdown, does not promote enzyme production under the conditions of this experiment. It was noted that both intra- and extracellular constitutive enzyme levels produced by cells growing on glucose (or by resting cells without inducer, Table IV) are less than 0.5% of the fully induced levels and thus are negligible. 

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. 

In terms of the carbon source, glucose is a catabolite repressor, but many oligomers and polymers of glucose induce enzyme production. Lactose, cellobiose, and sophorose are all dimeric sugars that induce cellulase production. Cellulose is also an inducer. A list of the performance of several carbon sources is found in Table 5 [37]. 

M. Mandels We are very interested in your results. In our experiments with Trichoderma viride we have had low yields of cellulase in 0.5-1.0% cellobiose culture, similar to your results with P. fluorescens. However, we could get excellent production of cellulase in these cultures when cellobiose consumption was slowed by sub-optimal temperatures, reduced aeration, or certain imbalances in the nutrients. We believe that high cellobiose levels repress cellulase formation. When the metabolic rate was decreased, however, the repression was relieved and cellobiose acted as an inducer. We believe, in fact, that cellobiose, the product of cellulase action, is the true inducer in a cellulose culture. Here the cellobiose is consumed by the fungus as rapidly as it is produced and never builds up to repressing levels. 

The role of cellobiose is complex (Figure 3). It is an inducer of cellulase, and can act also as an inhibitor of cellulase action (27). In addition, high concentrations (0.5-1.0%) of cellobiose or other rapidly metabolized carbon sources such as glucose or glycerol strongly repress cellulase formation (23, 24), so that cellulase does not normally appear... 

Cellobiose induces xylanase s3mthesis in some microorganisms [24], but sometimes, this enzyme is associated with cellulases. The crude enzymatic extract produced by B. circulans D1 on cellobiose is free of cellulases. This is important data that confirm the enzyme potential for application in biobleaching processes [6]. 

The principal features of a mathematical model described for the enzymatic hydrolysis and fermentation of cellulose by Trichoderma reesei are the assumption of two forms of cellulose (crystalline and amorphous), two sugars (cellobiose and D-glucose), and two enzymes (cellulase and j3-D-glucosidase). An inducer-repressor-messenger RNA mechanism is used to predict enzyme formation, and pH effects are included. The model consists of 12 ordinary differential equations for 12 state variables and contains 38 parameters. The parameters were estimated from four sets of experimental data by optimization. The results appear satisfactory, and the computer programs permit simulation of a variety of system changes. 

C12H20O11 340.283 Formed by microbial degradation of D-cellobiose. Potent inducer of cellulase in Trichoderma reesei. Cryst. (EtOH). 

Mycelia and ungerminated conidia of Neurospora crassa have been shown to secrete an entfo-cellulase. A simple induction system of phosphate buffer plus inducer relied on the internal metabolic reserves of conidia or mycelia to provide energy and substrates for protein synthesis. Cellobiose was the best inducer. In deionized water, the cellulase remained mostly associated with the cell, but a variety of salts stimulated the release of the enzyme into the medium. 

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