(11g) High-Yield and High-Titer n-Butanol Production From Lignocellulosic Biomass by Engineered Clostridium Tyrobutyricum

The cost of substrates and nutrients, including organic nitrogen source and carbon materials, is one of the key factors that could determine the development and application of biofuels as an alternative transportation fuel. In order to make the biofuels more cost-effective and competitive over petrochemical fuels, we investigated the utilization of corn steep liquor (CSL) and lignocellulosic biomass for n-butanol, a superior biofuel over bioethanol, production by a metabolically engineered Clostridium tyrobutyricum.  In general, a high n-butanol titer of ~17 g/L with a yield of 0.33 g/g glucose, 80% of the theoretical yield, was achieved in batch fermentation using corn steep liquor as the nitrogen source and glucose as the carbon source. Further improvements in n-butanol titer (~100 g/L) and yield (~0.35 g/g glucose) were achieved by applying integrated gas-stripping process for in situ butanol recovery and cell immobilization in a fibrous-bed bioreactor (FBB). Next, the feasibility of using various lignocellulosic biomass, including Jerusalem artichoke, cotton stalk, sugarcane bagasse, and corn fiber, as alternative feedstocks for fermentative n-butanol production was studied. The results showed that C. tyrobutyricum was able to efficiently convert lignocellulosic biomass hydrolysates containing glucose and xylose to n-butanol, achieving a high titer of over 15 g/L and a high yield of over 0.30 g/g substrate. This study demonstrated an economically competitive process for n-butanol production from abundant and renewable lignocellulosic biomass.