Abstract
Biofuels which can be produced by microorganisms from agricultural waste products will provide a renewable and non controversial source of energy for the future. The saccharolytic Clostridium sp. can ferment a wide range of sugars to produce organic acids and solvents. They are also anaerobic and in some cases thermophilic which is advantageous for large-scale industrial processes. C.pasteurianum shows potentially high solvent and hydrogen gas production capacity. The fermentation end products of C.pasteurianum, when grown in media of high sugar content, included significant quantities of acetone, butanol and ethanol, acetate, butyrate, CO2 and H2. The aim of this research was to investigate maltose uptake and metabolism in Clostridium pasteurianum NCIB 9486, to increase understanding of its starch utilisation. The organism was grown in different substrates and assayed for induction of glucosidase activities. Results confirmed that enzyme synthesis is induced by substrates.MaltaseandpNPGasewere found largely in soluble form (89.5% and 86.6% respectively) proving that maltase is produced intracellularly and hydrolysis of maltose takes place in the cytpoplasm. Fractionationof the soluble extract ofmaltose growncells yielded two maltase enzymes, maltase I (120-150 KDa) and maltase II (60 KDa). Further characterisation of maltase II showed high substrate specificity for maltose and its analogues, and sucrose. Maltase II exhibited similar rates of hydrolysis of maltose andmaltotriose: values for Km of 0.8 and 0.7 mmol l-1;Vmax of 3.3 and 4.2 nmol min-1, respectively. There is indication of specific activity of maltase II in cleaving the -1,4 (maltose) and -1,6-(isomaltose) linkages, but not -linkages (cellobiose). PEP-dependent phosphorylation of maltose was demonstrated suggesting the presence of a PEP-dependent PTS for maltose transport. This species has potential for use in biofuel production and a better understanding of its carbohydrate metabolism will facilitate its exploitation.
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