Bioabatement to remove microbial inhibitors from Miscanthus giganteus hydrolysates for enhanced butanol fermentation

The recalcitrant nature of cheap lignocellulose warrants pretreatment process to disrupt the lignin matrix and expose the carbohydrate fraction to enzymatic saccharification. Generation of lignocellulose-derived microbial inhibitory compounds (LDMICs) during the pretreatment process undermines large-scale utilization of biomass for biofuel (e.g. butanol) production. LDMICs are derived from lignin (e.g. vanillin), cellulose (e.g. 5-hydroxymethylfurfural [HMF]), and hemicellulose (e.g. acetic acid) fractions of lignocellulose. These compounds impair butanol fermentation by disrupting the growth of butanol-producing Clostridium beijerinckii through diverse mechanisms including perturbation of redox and energy state of the cell, inhibition of glycolytic enzymes, and damage to cell membrane, nucleic acids and organelles. Although LDMICs can be removed from lignocellulosic biomass hydrolysates (LBH) by physicochemical methods, these methods increase the overall butanol production cost. Bioabatement, a cost-effective alternative, employs microorganisms that selectively metabolize LDMICs in the presence of fermentable sugars. In this study, we demonstrate the ability of the bacterium, Cupriavidus basilensis ATCC®BAA-699 to metabolize pure LDMICs and Miscanthus giganteus biomass hydrolysate (MH)-associated LDMICs. Notably, MH was generated by dilute-acid (2% H2SO4) pretreatment at 15% biomass solids loading in a reactor at 180˚C and 150 psi for 1 h. The hydrolysate was then detoxified by C. basilensis prior to enzymatic hydrolysis to release fermentable sugars. Acetone-butanol-ethanol (ABE) fermentation of C. basilensis-detoxified MH resulted in ~70% increase in ABE concentration when compared to the non-detoxified control. These results underscore the feasibility of biological removal of LDMICs from pre-enzyme hydrolyzed LBH prior to fermentation to butanol.Ohio Plant Biotechnology Consortium (OPBC), Ohio Agricultural Research and Development Center (OARDC), and the Hatch grant (Project No. OHO01333