Ethanol Production

About

Applications: Ethanol from cellulose promises to provide a replacement for gasoline in greater quantity and at lower cost than ethanol from corn. The anaerobic bacterium Clostridium thermocellum is an excellent candidate for conversion of renewable cellulose biomass to ethanol because it is a robust thermophile with stable enzymes.   Advantages: The ideal organism to make ethanol from cellulose biomass will break down cellulose, ferment sugar, tolerate high concentrations of ethanol, and produce only ethanol. Research has focused on modifying organisms that already performs some of these functions by adding desired pathways and knocking-out undesirable ones. Clostridium thermocellum is a thermophile with cellulase genes. It is an ideal candidate for these genetic manipulations. Although C. thermocellum holds high promise, it has several shortfalls, including a branched fermentation pathways which produce acetate and lactate, along with ethanol. These byproducts limit conversion yield and are targeted for correction by genetic engineering with our technology. C. thermocellum uses a large number of enzymes to break down a range of biomass types, and a mechanism to selectively modulate the biosynethesis of these enzymes for a particular biomass material. By understanding how to regulate this gene cluster it is possible to shutdown or up regulate this pathway. The goal is to re-engineer C. thermocellum to express an abundance of particular genes so that it can efficiently produce ethanol from a particular biomass. Our technology is the first demonstration of cellulase genes that have been regulated by negative control. GlyR3 is targeted as a potential transcription regulator to provide control of gene expression. Laminaribiose is the inducer for the gene cluster which creates the LicA enzyme that degrades lichenan. The inducible system can be applied to not only Clostridium thermocellum but other bacteria with cellulase and hemi-cellulase genes.