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Researchers Develop New Bacterial Strain with Higher Butanol Tolerance; Potential to Double the Output of Biobutanol from Conventional Bacterial Fermentation

Researchers at Ohio State University and Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, have developed a method that can double the output of biobutanol compared to conventional bacterial fermentation through the use of a new strain of bacteria and a new bioreactor. They reported their results at the 238th national meeting of the American Chemical Society in Washington, DC.

Under conventional production in a bacterial fermentation tank, the high toxicity of butanol results in a low butanol titer (about 15 grams per liter); i.e., with increasing butanol concentration in the tank, the environment becomes too toxic for the bacteria to survive. This heavily affects the economics of biobutanol production.

Biobutanol has a number of advantages over ethanol for use as a biofuel—it is more hydrophobic; has a higher energy density; can be transported through existing pipeline infrastructure; and can be mixed with gasoline at any ratio.

To improve butanol tolerance of the organisms, Shang-Tian Yang, professor of chemical and biomolecular engineering at Ohio State, and his colleagues developed a mutant strain of the bacterium Clostridium beijerinckii in a bioreactor containing bundles of polyester fibers.

They immobilized cells of an asporogenous (non spore-producing) mutant of C. beijerinckii in the fibrous bed bioreactor (FBB). Culture medium and process conditions were optimized to facilitate the butanol production. Cells immobilized in the FBB were used as seeds for each subsequent batch of fermentation; thus, these cells were intermittently challenged with butanol produced by themselves.

After several fermentation batches’ adaptation, a mutant strain was isolated from the FBB. Compared with the original strain, the mutant showed higher butanol tolerance and reduced autolysis (self-destruction). At the same time, for the mutant, the fermentation conditions needed to realize the metabolic shift from acidogenesis to solventogenesis were different from that of its parent strain.

Under subsequently optimized fermentation conditions to maximize the butanol production potential of the mutant, the maximal butanol titer was improved to up to 30 grams per liter.

In addition, they constructed a recombinant C. beijerinckii strain with enhanced mutation frequency. They suggest that the mutator strain, in combination with the FBB-based adaptation method, will help more rapid evolution of the solvent-producing Clostridium beijerinckii towards higher butanol tolerance.

The engineers are applying for a patent on the mutant bacterium and the butanol production methodology, and will work with industry to develop the technology. This research is funded by the Ohio Department of Development.




If Butanol is hydrophobic, why not continuously skim the butanol from the vat? Is the density of butanol too close to that of water for gravimetric separation?

Henry Gibson

Perhaps a mutant human could be developed that would be willing to drive a low horsepower automobile. One might, with recombinant DNA technology, make one that could tolerate 60 mph driving on freeways in an efficient car.

With a great deal of effort a human might be able to be created that could understand that since he and all other live creatures and plants always have eaten radio-active foods and must themselves be radio-active and that every square foot of earth has always had uranium or other radioactive elements in it, that he can survive some radioactivity. ..HG..

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