Abstract: Clostridium sp. are an obligate anaerobic bacterium that produces butyric acid as its major end-product. Previously, we have developed an integrated process that couples fermentation of biomass sugars, with in situ product recovery and distillation. This process works best at pH's lower than 7.0. The process serves to extract carboxylic acids during fermentation which enables reduced base-loading and reduced end-product toxicity. Disclosed herein are methods and non-naturally Clostridium sp. that are capable of increased production of butyric acid and increased growth at low pH conditions (e.g., pH<5.0).