Microbial inhibitors arise from lignin, hemicellulose, and degraded sugar during pretreatment
of lignocellulosic biomass. The fungus Coniochaeta ligniaria NRRL30616 has native
ability to metabolize a number of these compounds, including furan and aromatic aldehydes
known to act as inhibitors toward relevant fermenting microbes. In this study, C.
ligniaria was used to metabolize and remove inhibitory compounds from pretreated rice
hulls, which comprise a readily available agricultural residue rich in glucose (0.32e0.33 g
glucan/g hulls) and xylose (0.15e0.19 g xylan/g hulls). Samples were dilute-acid pretreated
and subjected to bioabatement of inhibitors by C. ligniaria. The bioabated rice hull hemicellulose
hydrolyzates were then utilized for ethanol fermentations. In bioabated liquors,
glucose was converted to 0.58% (w/v) ethanol by Saccharomyces cerevisiae D5a at 100% of
theoretical yield, while fermentations of unabated hydrolyzates either failed to exit lag
phase or had reduced ethanol yield (80% of theoretical). In fermentations using ethanologens
engineered for conversion of pentoses, bioabatement of hydrolyzates similarly
improved fermentations. Fermentation of xylose and arabinose by ethanologenic Escherichia
coli FBR5 yielded 2.25% and 0.05% (w/v) ethanol from bioabated and unabated samples,
respectively. Fermentations using S. cerevisiae YRH400 had decreased fermentation lag
times in bioabated hydrolyzates. However, xylose metabolism in S. cerevisiae YRH400 was
strongly affected by pH and acetate concentration.