Impact of pretreatment inhibitors on microorganisms for advanced biofuel production

Although the effect of inhibitors generated from various pretreatment and hydrolysis processes on ethanologenic microorganisms is well known, we have limited information of the impact of these pretreatment inhibitors on hydrocarbons and/or intermediate-producing microorganisms. In this study, we carried out a detailed analysis of saccharified slurries from both pretreated cornstover and deacetylated pretreated cornstover using various analytical techniques such as Inductively-Coupled Plasma Mass Spectrometry (ICP-MS), Gas Chromatography–Mass Spectrometry (GC-MS), and Liquid Chromatography with Diode-Array Detection and Mass Spectrometry (LC-DAD-MS) to identify compounds present that could inhibit the growth of potential hydrocarbon producingn strains. Eleven potential toxic compounds identified at highest concentrations and their potential derivatives were investigated for their impact on four bacterial species with the potential to produce hydrocarbons and/or intermediates, which include ammonium acetate and ammonium sulfate as the most abundant cations; two sugar degradation products of furfural and HMF; and seven lignin monomers of 4-hydroxybenzaldehyde, vanillin, benzoic acid, p-coumaric acid, ferulic acid, 4-hydroxybenzoic acid, and vanillic acid. Toxicity profiles were generated and the top inhibitors identified for Rhodococcus opacus, Cupriavidus necator, E. coli, and Zymomonas mobilis. Furfural and acetate are the most toxic compounds for all strains tested with furfural more toxic than acetate. In addition, genomic studies were initiated to understand the bacterial toxicity profiles and to propose genetic targets for metabolic engineering to improve strain robustness or substrate utilization.