ABSTRACT
The fundamental challenge in selecting or tailoring a microorganism to produce ethanol from the mixture of sugars resulting from the hydrolysis of lignocellulosic feedstocks is easily articulated: the best ethanol producers are incompetent at utilizing pentose sugars (including those that are major components of hemicelluloses, that is, d-xylose and l-arabinose), whereas species that can ef ciently utilize both pentoses and hexoses are less ef cient at converting sugars to ethanol, exhibit poor tolerance of high ethanol concentrations, or coproduce high concentrations of metabolites such as acetic, lactic, pyruvic, and succinic acids in amounts to compromise the ef ciency of substrate conversion to ethanol.1-4
Because bioprospecting microbial species in many natural habitats around the global ecosphere has failed to uncover an ideal ethanologen for fuel ethanol or other industrial uses, considerable ingenuity has been exhibited by molecular geneticists and fermentation specialists in providing at least partial solutions for the two most popular “combinatorial biology” strategies of
Endowing traditional yeast ethanologens with novel traits, including the ability to utilize pentoses “Reforming” bacterial species and nonconventional yeasts to be more ef - cient at converting both pentoses and hexoses to ethanol
A third option, that is, devising conditions for mixed cultures to function synergistically with mixtures of major carbon substrates, is discussed in chapter 4 (section 4.5).
