In addition to fermenting multiple sugars, effective lignocellulosic biocatalysts must also withstand biological inhibitors created during pretreatment and hydrolysis of biomass. One of the critical inhibitors is acetic acid, which forms during xylan de-acetylation. Acetic acid can negatively impact growth, productivity, and titer at concentrations encountered in the biomass to ethanol process, especially in the pH range typical for industrial fermentations.
Here we describe a synthetic pathway created in T. saccharolyticum for the conversion of acetic acid to the solvents acetone and isopropanol. Acetone and isopropanol are less inhibitory than acetic acid, and can be recovered as products by distillation or gas stripping. T. saccharolyticum ethanologen strains carrying the acetate conversion pathway show increased ethanol titers from sugar/acetic acid mixtures, and under some conditions do not require base addition to neutralize pH during fermentation.