Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637952
Title: Biosynthesis of the cellulase complex in fungi, with special reference to Trichoderma koningii
Author: Lovelady, J. A.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1980
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Abstract:
The work presented in this thesis is a study of the growth of Trichoderma koningii in both batch and continuous culture with a special interest in the biosynthesis and regulation of two of the enzymes of the cellulase complex, CM-cellulase and P-glucosidase. CM-cellulose with a degree of substitution of 0.7-0.8 has been shown to be a useful substrate for the synthesis of the two enzymes under study. CM-cellulose was shown to offer 23% of its theoretically available sugar to the organism for utilisation. The production of both CM-cellulase and P-glucosidase is about three-fold greater in continuous culture in fermenters than under similar conditions of batch culture. In batch culture, it has been possible to increase the yield of each enzyme independently of one another, but not simultaneously. Thus, replenishing spent medium in a batch culture improves the density of the culture, but only the yield of P-glucosidase. Aeration of the culture has been shown to be important, particularly for CM-cellulase formation; thus in batch culture, decreasing the aeration rate to + vol/vol from the usual rate of I vol/vol increased the yield of this enzyme threefold and brought it close to the yields found in culture. Under conditions of continuous culture, where autolysis of cells would be minimal, it was found that CM-cellulase was a wholly extracellular (about 99%) enzyme whereas P-glucosidase was almost entirely intracellular (at least 90%). In continuous culture, but not in batch, CM-cellulase has been shown to be an inducible enzyme and can be induced by low concentrations of cellobiose as sole carbon source, but higher concentrations became repressive. In both batch and continuous culture the synthesis of this enzyme was very sensitive to repression by metabolites of cellulose such as glucose and glycerol, for instance, glucose at concentrations as low as up to 30 pg/ml was a very effective repressor of CM-cellulase synthesis when added to the continuous inflow of CM-cellulose. P-glucosidase has also been shown to be induced by cellobiose, but in batch as well as in continuous culture and by high as well as low concentrations of the sugar. The induction is brought about by growing the organism on gradually increasing concentrations of the sugar (in continuous culture) and in absence of other carbon sources such as CM-cellulose. Higher concentrations of cellobiose or a change of substrate to glucose or glycerol caused repression. The use of a continuous inflow of low concentrations of either glucose (30 )ag/ml) or cellobiose (IO fag/ml) has shown the sensitivity of both of these enzymes to these sugars and also made it possible to study their control without the use of large amounts of such sugars; the latter causes excessive increase in cell weight and lowering of the pH, both of which can complicate interpretations of control mechanisms involving these sugars and their effects on enzyme synthesis. Based on the above results a scheme has been proposed for the action of metabolic products of cellulose, such as cellobiose and glucose, in regulating the biosynthesis of CM-cellulase and P-glucosidase and thus the overall breakdown of cellulose itself.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.637952  DOI: Not available
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