Comprehensive investigations of biobutanol production by a non-acetone and 1,3-propanediol generating Clostridium strain from glycerol and polysaccharides

Background: Low-cost feedstocks, a single product (butanol), and a high butanol titer are three key points for establishing a sustainable and economically viable process for biological butanol production. Here, we comprehensively investigated the butanol production from mono-substrates, mainly glycerol and polysaccharides, mainly starch and xylan by a newly identified wild-type Clostridium pasteurianum GL11. Results: Strain GL11 produced 14.7 g/L of butanol with a yield of 0.41 g/g from glycerol in the batch mode without formation of by-products of acetone and 1,3-propanediol (1,3-PDO). With in situ extraction with biodiesel, the amount of butanol was finally improved to 28.8 g/L in the fed-batch mode. Genomic and enzymatic analysis showed that the deficiency of key enzymes involved in acetone and 1,3-PDO pathway within strain GL11 led to the elimination of these by-products, which may also greatly simplify downstream separation. The elimination of acetone and 1,3-PDO and high butanol tolerance contributed to its high butanol production yield from glycerol. More importantly, strain GL11 could directly convert polysaccharides, such as xylan and starch to butanol with secretion of xylanase and amylase via consolidated bioprocessing. Conclusions: The wild-type strain GL11 was found to be particularly advantageous due to its capability of efficient butanol production from glycerol and polysaccharides with elimination of acetone and 1,3-PDO formation. And the high butanol production with in situ extraction by using biodiesel would significantly enhance the economic feasibility of fermentative production of butanol from glycerol. These unique features of C. pasteurianum GL11 open the door to the possibility of cost-effective biofuels production in large scale.