Masters Degrees (Microbiology)

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Browsing Masters Degrees (Microbiology) by Subject "Acremonium cellulolyticus"

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    Cloning and expression of a β-glucosidase gene from Acremonium cellulolyticus in Saccharomyces cerevisiae
    (Stellenbosch : Stellenbosch University, 2013-03) Nel, De Wet Andries; Volschenk, Heinrich; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Humanity is currently dependant on fossil fuels as an energy source. Increasing economic development and industrialization is, however, raising the demand for this unsustainable energy source. This increased pressure on dwindling reserves and growing concern over detrimental environmental effects associated with the use of these fuels have sparked great interest in the development of alternative sources. Bioethanol has surfaced as a good alternative to fossil fuels, as it can be produced from cheap, abundant, renewable, non-food sources. Bioethanol is also carbonneutral, i.e. utilisation thereof leaves the net level of carbon dioxide in the atmosphere unperturbed. Lignocellulose, more specifically its cellulose fraction, has been identified as a possible feedstock for the production of bioethanol. The use of lignocellulose as feedstock will allow for a more sustainable supply and much needed energy security. Lignocellulosic feedstocks can be divided into two main categories, i.e. wastes from processes other than fuel production and crops grown specifically for fuel production. Cereal crops such as triticale have been identified as good industrial crops for the production of energy. Triticale’s higher biomass yield, moderate water and nutrient requirements, steadily increasing area of cultivation and main use as an animal feed and not a human food source, makes it attractive as feedstock for the production of bioethanol. The combined activity of endoglucanases, exoglucanases and β-glucosidases is needed to hydrolyse crystalline cellulose to fermentable sugars. The high cost of these enzymes is, however, the most significant barrier to the economical production of bioethanol from cellulosic biomass. A promising strategy for a reduction in costs is the production of these cellulolytic enzymes, hydrolysis of biomass and fermentation of the resulting sugars to bioethanol in a single process step via a cellulolytic microorganism. The development of such a consolidated bioprocessing (CBP) organism can be achieved by the introduction of cellulolytic activity into a noncellulolytic microorganism that is able to ferment glucose to ethanol. Saccharomyces cerevisiae is a good host candidate for CBP as this yeast’s high tolerance towards ethanol and its use in industrial applications has been established. The enzymatic activities of endoglucanases and exoglucanases are, however, inhibited by the build-up of cellobiose during the hydrolysis of cellulose. This effect may be alleviated with the introduction of a better functioning β-glucosidase into the system. β-Glucosidases hydrolyse cellobiose to glucose, alleviating the inhibition on the enzymatic activities of endoglucanases and exoglucanases. Despite advances in enzyme production systems and engineering enzymes currently in use for higher stability and activity, there is still a demand to expand the current collection of enzymes. Bioprospecting for novel cellulolytic enzymes focuses on specific environment, with high turnover rates of cellulosic material or extreme conditions, such as the composting process. These enzymes are becoming more attractive compared to their mesophillic counterparts due to their potential industrial applications and the fact that they represent the lower natural limits of protein stability.