Bacteria turned into biofuel factories

Michael Barnes / UC Berkeley

Graduate student Brooks Bond-Watts and post-doctoral fellow Jeff Hanson examine cultured E. coli used to produce the biofuel n-butanol.



By John Roach

Researchers have genetically engineered the bacteria E. coli to produce a gasoline-like biofuel called n-butanol at a rate that is about 10 times better than competing systems.

N-butanol (normal butanol) is naturally made by various species of the bacteria Clostridium. Since the 1920s, researchers and industry have genetically tweaked these bacteria to boost their butanol-producing abilities, said Michelle Chang, a chemist at the University of California at Berkeley.

“We were asking a different question: Can you take a microbe that is easy to work with in the lab and also easy to grow on an industrial scale and reprogram it to do new chemistry and can you compete … with the native organisms they’ve optimized,” she told me Wednesday.

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E. coli tweaks To find out, as in earlier efforts, Chang and her colleagues inserted Clostridium genes into E. coli. But to get better yields than previous efforts, they replaced two of the enzymes in the Clostridium material with look-alike enzymes from other organisms.

The tweak helped the team overcome one of the main obstacles with Clostridium: It makes butanol, but also unmakes it. “They can turn it back to whatever it started with,” Chang explained. “So it is really important if you want to build up high levels (of fuel) to put in a block where it can’t go back.”

The two enzyme substitutes serve as that block, leading to nearly five grams of butanol per liter of cells — that’s 10 times more butanol than produced by other strains of genetically engineered E. coli and yeast.

The genetically engineered E. coli is only about one third the production as the best genetically engineered Clostridium, but Chang believes researchers have hit a ceiling in terms of what they can do with the native organism.

“If you think about the native organism, it makes butanol for its own purposes, not to make the most possible,” she said. “But if we take a genetically tractable organism, we can better optimize it for something it doesn’t already do.”

The team has already improved on previous efforts with E. coli and thinks that with further tweaks they can get up to a four-fold increase in efficiency from where they are today.

Green future Chang said the use of genetically engineered bacteria to produce butanol is “green” for two reasons. First, eventually, the feedstock for the bacteria would be plant material, a renewable resource for biofuels, which, in theory, leads towards a carbon neutral balance.

In addition, this is also green from a synthetic chemistry point of view, she noted.

“There’s a huge amount of chemical waste that is related to the way we make molecules, so what we are interested in is asking can you do chemistry inside a living organism?” she said. “Then it is all in water and it is all based on naturally occurring systems.”

More stories on butanol:

* W2 begins to construct biobutanol reactor * Bacteria rebuilt to make oil * Mutant bacteria + polyester = more biofuel * The race to replace gasoline

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A paper describing the research appeared online this week in the journal Nature Chemical Biology. In addition to Chang, co-authors include graduate student Brooks B. Bond-Watts and recent UC Berkeley graduate Robert J. Bellerose.

John Roach is a contributing writer for Connect with the Cosmic Log community by hitting the “like” button on the Cosmic Log Facebook page or following’s science editor, Alan Boyle, on Twitter (@b0yle).


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