Exploring Ethanol Biofuel Production using the Bacterium Clostridium thermocellum

Composting plant matter to produce fertilizer relies on the combined effort of bacteria and insects to eat, and chemically change, the plant material. Cellulose, a major component of plants, can be converted not only into fertilizer, but also into biofuel (fuel made by biological organisms), which is becoming a commercially valuable product. In recent work, Dr. Ranjita Biswas and her team in the United States studied the conversion of cellulose to the industrial biofuel ethanol by the bacterium Clostridium thermocellum. If C. thermocellum produces too much ethanol it’s growth is inhibited, resulting in only low yields of ethanol. Therefore, C. thermocellum was genetically altered to survive in the presence of higher levels of ethanol. This goal was achieved by preventing the production by these altered cells of a different product (explained below). Despite these promising findings, however, their altered version of C. thermocellum would still be poisoned by the high ethanol concentrations found in industrial settings. This work demonstrates that it is often difficult to alter the way bacteria behave.

Screen Shot 2017-08-12 at 4.33.09 PM This figure shows the pathway to convert cellulose into ethanol. Each arrow represents the step or steps (multiple arrows) to get from one compound to another. Cellulose is first converted to glucose (through multiple steps), and then glucose is converted to pyruvate. At this point, pyruvate can either be converted into lactate or acetyl-CoA (depending on what the cell needs). The researchers eliminated the ability of the cell to convert pyruvate into lactate so only acetyl-CoA was made. Then acetyl-CoA can be converted into acetate or ethanol!

Summary written by: Emma Finlayson-Trick

To read the full paper, please click the following link:

Increase in Ethanol Yield via Elimination of Lactate Production in an Ethanol-Tolerant Mutant of Clostridium thermocellum”

Ranjita Biswas, Sandeep Prabhu, Lee R. Lynd, Adam M. Guss


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