Its metabolic characteristics suggest Zymobacter palmae gen. Nov., sp. Nov. could serve as a useful new ethanol-fermenting bacterium, but its biotechnological exploitation will require certain genetic modifications. We therefore engineered Z. palmae so as to broaden the range of its fermentable sugar substrates to include the pentose sugar xylose. The Escherichia coli genes encoding the xylose catabolic enzymes xylose isomerase (XI), xylulokinase (XK), transaldolase (TA) and transketolase (TK) were introduced into Zb. palmae, where their expression was driven
by the Zymomonas mobilis glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter. When cultured with 40 g/l xylose, the recombinant Z. palmae was able to ferment 16.4 g/l xylose within 5 days, producing 91% of the theoretical yield of ethanol with no accumulation of organic acids as metabolic by-products. Notably, xylose-acclimation enhanced both the expression of xylose catabolic enzymes and the rate of xylose uptake into recombinant Z. palmae, which enabled the acclimated organism to completely and simultaneously ferment a mixture of 40 g/l glucose and 40 g/l xylose within 8 h, producing 95% of theoretical yield of ethanol. Thus, efficient fermentation of a mixture of glucose and xylose to ethanol can be accomplished using Z. palmae expressing E. coli xylose catabolic enzymes.
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by the Zymomonas mobilis glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter. When cultured with 40 g/l xylose, the recombinant Z. palmae was able to ferment 16.4 g/l xylose within 5 days, producing 91% of the theoretical yield of ethanol with no accumulation of organic acids as metabolic by-products. Notably, xylose-acclimation enhanced both the expression of xylose catabolic enzymes and the rate of xylose uptake into recombinant Z. palmae, which enabled the acclimated organism to completely and simultaneously ferment a mixture of 40 g/l glucose and 40 g/l xylose within 8 h, producing 95% of theoretical yield of ethanol. Thus, efficient fermentation of a mixture of glucose and xylose to ethanol can be accomplished using Z. palmae expressing E. coli xylose catabolic enzymes.
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