Genetic Engineering and Butanol Fermentation

Environmental concerns and non-renewable nature of fossil fuels has triggered research interest in biofuel production from lignocellulosic biomass. Biofuel production explores two main routes which are biochemical and thermochemical pathway. Biochemical pathway is concerned with the use of chemicals, enzymes and microbes during biofuel production while thermochemical pathway address processes like pyrolysis, gasification and combustion to produce syngas of producer gas.

However, a hybrid technology that explores the combination of the biochemical and thermochemical pathway was recently developed via syngas fermentation. Butanol is a valuable biofuel and has the potential to replace gasoline due to its energy content. Focusing on the biochemical pathway, microbes are an integral part of butanol production via ABE fermentation. Clostridia species has been utilized for Acetone Butanol and Ethanol (ABE) fermentation. However, production concentration has been widely affected by inhibitors in the hydrolysate, substrate and butanol toxicity. The purpose of this study is to discuss the recent advancement on the genetic manipulation of clostridium species to optimize butanol production.

Butanol fermentation is an age long technology which started in the early twentieth century while using molasses as substrates via the ABE fermentation. Clostridia have the capabilities to produce butanol from a range of substrates like food crops such as corn, sugarcane and cassava, they also utilize non-edible substances such as switchgrass, food wastes, wood and bagasse. Species of clostridia that have been used for ABE fermentation are Clostridium beijerinckii, Clostridium acetobutylicum, Clostridium pasteurianum, clostridium difficile, Clostridium tetani, Clostridium botulinum, and Clostridium saccharobutylicum among others. Furthermore, Clostridium beijerinckii and Clostridium acetobutylicum is the most widely used. Clostridia species first produce organic acids during to acidogenic phase which results to a lower pH that triggers a switch to the solventogenic phase when the solvents will be produced.

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