T. K. Ghose

Biodegradation of cellulosic materials: Substrates, microorganisms, enzymes and products

Abstract Cellulosic materials are the only renewable resources available in large quantities which need to be properly utilized to meet our needs of energy, chemicals, food and feed for a long-range solution. A variety of lignocellulosic materials are available and microorganisms capable of degrading either one or more of the three main constituents, viz. cellulose, hemicellulose and lignin have been studied. At least three different enzymes of the multicomponent cellulase system, i.e. cellobiohydrolase endo-glucanase and β-glucosidase are involved in the degradation of crystalline cellulose into glucose. Their mode of action and the manner in which they bring about hydrolysis of crystalline cellulose is discussed in detail. The involvement of parallel enzymes for hemicellulose degradation is also known to some extent but needs to be studied more elaborately, independently and in combination with cellulases. The potential of cellulosic biomass as a source of fuel and petroleum-sparing substances is also reviewed.

Bioethanol in India: Recent Past and Emerging Future

There is renewed interest in bioethanol technology in view of its large potential as a transportation fuel. Bioethanol production based on lignocellulosic biomass, being the technology of the future, has been examined. The major issue is the production of ethanol at a competitive price. Biomass-based ethanol technologies are still evolving and the commercialization of this technology has to overcome various bottlenecks. Keeping this perspective in view, bioethanol technologies are analyzed in terms of feedstock availability, pretreatment strategies, efficient hydrolytic agents, availability of recombinant ethanologens and process economics with a focus on Indian research efforts. It provides indicators for research priorities to achieve these objectives.

Studies on mixed fungal culture for cellulase and hemi-cellulase production part-1: Optimization of medium for the mixed culture ofTrichoderma reesei D1-6 andAspergillus Pt 2804

SummaryFor enhanced production of cellulase and xylanase by the mixed culture ofT. reesei D1-6 andA. wentii Pt 2804, the composition of medium has been optimized.

Effect of l(–)Sorbose on the Release of β-Glucosidase by Trichoderma reesei QM9414

Summary: l(–)Sorbose, a sugar known to cause paramorphogenesis in fungi, was tested for its effect on morphology and release of cell-wall bound β-glucosidase (EC 3.2.1.21) in the cellulolytic fungus Trichoderma reesei QM9414. Sorbose caused an increase in branching and septation in the growing mycelium. Extracellular β-glucosidase activity was enhanced when cellobiose or cellulose growth medium was supplemented with sorbose. In sorbose-supplemented cultures, the β-glucosidase activity associated with the wall fraction was less than half that in unsupplemented cultures. The intracellular activity was also lower in the sorbose-supplemented cultures than in unsupplemented controls. The glucosamine/glucose ratio of wall hydrolysates from sorbose-supplemented cultures was about twice that of control hydrolysates. Since β-glucosidase is closely associated with 1,3-β-glucan in the walls of T. reesei, a decrease in wall glucan content, and the resulting weakened association of the enzyme with the walls, is probably responsible for its increased release into the culture medium in the presence of sorbose.

Studies on fibre-entrapped whole microbial cells in urea hydrolysis

Abstract Microbial cells possessing high urease activity were entrapped in cellulose triacetate fibres, and their capability to hydrolyse urea was evaluated. The activity obtained using these fibres was found to be dependent on the amount of cells entrapped; the best cells-to-carrier ratio was 1:10. Optimum pH and optimum temperature were 7.2 and 60°C respectively, for both the free cells and the immobilized cells, which suggests that the cells are physically bound to the polymer matrix. The effect of flow rate on the extent of conversion and continuous hydrolysis of urea was examined. A flow rate corresponding to a residence time of 1.325 h was found to be satisfactory. The computed half-life of the system was 177.7 h. The potential industrial application is also discussed.

Localization and release mechanism of cellulases in Trichoderma reesei QM 9414

SummaryA significant increase in the extracellular yield of β-glucosidase was observed when Trichoderma reesei QM 9414 was cultivated on a cellulose medium containing chitin. Measurement of enzyme activities in the various fractions of the mycelium revealed that endoglucanase was truly extracellular while β-glucosidase was cell wall bound. Treatment of Trichoderma mycelium with cell wall degrading enzymes (produced from Trichoderma) led to a release of β-glucosidase from the mycelium. Apparently chitin, in the presence of cellulose, induces the synthesis of chitinase and other cell wall lytic enzymes which promote release of the intramural β-glucosidase into the medium.

Effect of L(---)Sorbose on Cellulase Activity in Trichoderma reesei QM9414

SUMMARY: L(---)Sorbose enhanced the extracellular levels of endoglucanase and filter paper unit activity in culture filtrates of Trichoderma reesei QM9414 cultivated on cellobiose or Avicel cellulose. Addition of sorbose to the culture medium retarded the uptake of cellobiose by the organism; this uptake appeared to be dependent on the surface-bound β-glucosidase. A biochemical mechanism to explain the effect of sorbose on cellulase induction, through its effect on surface-bound β-glucosidase and cellobiose uptake, is proposed.

Growth and enzyme production by Polyporus hirsutus in presence of ammonium sulphate

SummaryGrowth of Polyporus hirsutus on rice straw rapidly increases its susceptibility to cellulase and xylanase. Addition of ammonium sulphate to the straw (0.1 g/g) enhances cellulase and xylanase production but does not affect laccase production by the fungus although it appears to inhibit its growth.

Biotechnology in India I

Conventional biotechnology based industries are already established economic activities in India. Facilities have also been set up for the production of restriction endonucleases, oligonucleotides, culture media, plastic wares, micro pipettes etc., However recombinant biotechnology products are still at the research stage and market demand is met through imports. The bulk of the R & D resources for product development are currently being provided by the Government, which has also taken steps to develop trained man power, set up the infrastructure for research, and has organised demonstration projects for faster dissemination of research results to industry. The consumption of biotech products will rise from Rs. 18.74 billion in 1992 to Rs. 55.47 billion in 2000 and the expected additional investment is anticipated to be Rs. 14 billion during the next 8 years.