Induction of cellulases

The induction of this operon responds to the intracellular concentration of cAMP, which is determined by the carbon source available to the cell. When cells are grown on cellobiose or cellulose that do not inhibit adenylate cyclase, cAMP is made in sufficient quantities for induction of cellulase. On the contrary, when cells are grown on glucose or other readily metabolized carbohydrates that do inhibit adenylate cyclase. 

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). 

The relationship between catabolite repression by glucose and induction of cellulase by sophorose has been studied in T. viride by Nisizawa and co-workers (36, 37). The induction by sophorose (10 M) was competitively repressed by glucose and other metabolites such as pyruvate. Since glucose was an effective repressor when added one hour after the previous addition of actinomycin D, it was concluded that the repression takes place at the translational level. Previous work indicated (26) that the sophorose induction led to the formation of a cellulase component designated FII, which is the source of cellulase II discussed below. In higher plants indoleacetic acid (38) and abscisic acid (39) have been shown to stimulate cellulase production. 

From a critical study of the metabolism of poly (A) in auxin-treated pea epicotyl, Verma and Maclachlan (73) showed that discreet classes of poly (A) (presumably part of mRNA s) are differentially associated with free and membrane-bound polysomes. The induction of specific mRNA s, the decline in the rate of synthesis of mRNA s, the polysome content per cell, and the formation of cellulase were all related to the membrane-bound polysomes. Although the rate of in vivo enzyme synthesis is... 

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. 

Soluble inducers are valuable in basic studies aimed at elucidating the nature of cellulase induction. As yet we have not found a good method to use them to obtain large quantities of cellulase. For producing cellulase on a large scale, the fungus is grown on cellulose. 

The induction of jS-o-glucosidase activities in Sporotrichum pulverulentum by cellulose and cellobiose has been investigated (see p. 410). A new source of cellulase used by Macrotermitinae has been described. Ingested conidiophores of the symbiotic fungus Termitomyces species provide this cellulase. ... 

T. reesei also contains a plasma-membrane-bound P-glucosidase of 70 kDa and IP 8.4 [126], which reacts with monoclonal antibodies against the 80 kDa enzyme [47]. This enzyme probably plays a role in the mechanism of cellulase induction [127, 128] however, it may also be an intermediate of the P-glucosidase secretory pathway. 

Most of the enzymes for plant cell wall degradation including cellulases and hemiceUulases are nsnaUy only formed adaptively in the presence of their substrates. Therefore effective sensing and signaling networks mnst be present to communicate the presence of the snbstrate to the fungus. As a consequence, induction of the different... 

Harman GE, Kubicek CP (1998) Trichoderma and Gliocladium, enzymes, biological control and commercial applications, vol 2. Taylor Francis Ltd., London Hartl L, Kubicek CP, Seiboth B (2007) Induction of the gal pathway and cellulase genes involves no transcriptional inducer function of the galactokinase in Hypocrea jecorina. J Biol Chem 282 18654-18659... 

The production of cellulases by bacteria is governed by induction, catabolism repression, or end product inhibition (Kumar et al. 2008). The former mechanism also controls the constitution of cellulosome from C. thermocellum. The proteo-mic maps of the cellulose-bound protein fraction containing the cellulosomes show that the enzymatic subunits vary according to the carbon source used in the culture medium (Raman et al. 2009 Natafet al. 2010). 

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