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Researchers tweak microbe to turn carbon dioxide into isobutanol
By Sue Retka Schill | August 30, 2012

Ralstonia eutropha converts carbon into a bioplastic, seen here as the light-colored dots inside the membrane. An engineered version produces isobutanol, which is expelled from the cells into the surround liquid.
Massachusetts Institute of Technology...

Scientists at Massachusetts Institute of Technology have taught a microbe a new trick, turning carbon dioxide into isobutanol. In nature, the wild soil bacterium Ralstonia eutropha turns fatty acids and other carbon compounds into a polymer, which is similar to a lot of petroleum-based plastics, explains Christopher Brigham, a research scientist in MIT’s biology department. Working with the native genes and inserting a gene from another organism, Brigham and his colleagues were able to redirect the microbe to make fuel instead of plastic.

“We’ve shown that, in continuous culture, we can get substantial amounts of isobutanol,” he said. He estimates that it will take up to five years to optimize the system. For one, the yield from the organism needs to be increased by five- or 10-fold to be viable, he said. The MIT team is also working on a continuous process to draw the isobutanol off. “We are working with a chemical engineer at Michigan State University to design a combination bioreactor and isobutanol isolation system,” Brigham said. “It’s a novel system where we can grow the cells more or less continuously and siphon away the spent media containing the alcohol and recover the alcohol in a cost-effective way, through distillation or some other process.”

More work is also being done on identifying other products, said co-author Jingnan Lu, graduate student in chemistry. “We’re taking away the native carbon storage system, to produce isobutanol as an example,” she said. “But in the future we are looking at making other useful compounds.” Some of those are alcohol-based, such as butanol. There is also a possibility that the microbe could be used for remediation for contaminants such as PCB. The scientists will also look at using carbon streams other than carbon dioxide, such as waste carbon streams from food processing or agriculture.

Brigham and Lu are co-authors in a paper, “Studies on the production of branched-chain alcohols in engineered Ralstonia eutropha,” published recently in the journal Applied Microbiology and Biotechnology.