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Title: CHARACTERIZATION OF A UNIQUE ETHANOLOGENIC YEAST CAPABLE OF FERMENTING GALACTOSE

Author
item KEATING, JEFFREY - UNIV BRITISH COLUMBIA
item ROBINSON, JAMIE - UNIV BRITISH COLUMBIA
item BOTHAST, RODNEY - RETIRED ARS EMPLOYEE
item SADDLER, JOHN - UNIV BRITISH COLUMBIA
item MANSFIELD, SHAWN - UNIV BRITISH COLUMBIA

Submitted to: Enzyme and Microbial Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2004
Publication Date: 6/1/2004
Citation: Keating, J.D., Robinson, J., Bothast, R.J., Saddler, J.N., Mansfield, S.D. 2004. Characterization of a unique ethanologenic yeast capable of fermenting galactose. Enzyme and Microbial Technology. 35:242-253.

Interpretive Summary: Biomass resources, like agricultural by-products and residues, wood, and municipal solid waste, have the potential to serve as substrates for production of fuel ethanol in much greater quantities than is currently produced from corn. However, these sources are composed of complex mixtures of sugars which are inefficiently fermented to alcohol. In the current study, a unique yeast was identified that could efficiently ferment galactose to ethanol. This strain was able to ferment very high concentrations of galactose (>225 g/L) and completely utilized all of this sugar in less time than typically required by other yeast strains. Further characterization of fermentation by this strain demonstrated that it used sugars in a non-regulated pattern. This information will be used to direct further development of the galactose fermenting strain for industrial application and the potential for use of combinations of yeasts in the bioconversion of biomass to ethanol.

Technical Abstract: The hexose and pentose sugars common to substrate mixtures used in yeast-catalyzed industrial processes are often affected by carbon catabolite repression, in which the presence of glucose significantly delays the consumption of other sugars. Screening experiments performed with wild-type Saccharomyces cerevisiae strains have identified a strain that exhibits exceptional fermentative performance on galactose, completely exhausting the sugar in significantly less time (6 h) than that typically required by other S. cerevisiae strains tested (10-24 h). This strain was also capable of initiating fermentation at very high concentrations of galactose (>225 gL**-1). Further experiments on mixed hexose sugar substrates (galactose, glucose, and mannose) indicated the absence of conventional catabolite repression in this strain, including a preference for galactose as carbon source and notable delays in the utilization of glucose and mannose. Additionally, the endogenous formation of extracellular glucose was observed during double sugar fermentations of galactose and mannose. Subsequent experiments illustrated differences between the selected strain and a reference strain in UDP-glucose-4-epimerase activity and suggested other unique molecular properties.