E. coli and K. oxytoca naturally metabolize arabinose,
such that the ethanologenic strains ferment all lignocellulose-
derived sugars [40]; furthermore, xylose- and arabinose-
fermenting strains of Z. mobilis have been
constructed [41]. Because yeast only ferment arabinose
to ethanol in rich media [42,43], S. cerevisiae has been
engineered for arabinose use by introducing both bacterial
[44] and fungal genes [45] encoding arabinose-metabolizing
enzymes, where the fungal approach did not result
in appreciable arabinose fermentation. The functional
arabinose-metabolizing pathway has recently been