Biofuels created at breakneck speed

RICE (US) — Engineers have discovered a new way to convert simple glucose into biofuels and petrochemical substitutes. The approach is up to 10 times faster than previous methods.

In a paper published online in Nature, the researchers described how they reversed one of the most efficient of all metabolic pathways—the beta oxidation cycle—to engineer bacteria that produce butanol, a biofuel that can replace gasoline in most engines.

“That’s really not even a fair comparison because the other organisms used an expensive, enriched feedstock, and we used the cheapest thing you can imagine, just glucose and mineral salts,” says Ramon Gonzalez, associate professor of chemical and biomolecular engineering at Rice University and lead co-author.

Graduate student Clementina Dellomonaco worked with Professor Ramon Gonzalez to create a new method for converting simple glucose into biofuels and petrochemical substitutes. (Credit: Jeff Fitlow)

“We call these ‘drop-in’ fuels and chemicals, because their structure and properties are very similar, sometimes identical, to petroleum-based products,” he says. “That means they can be dropped in, or substituted, for products that are produced today by the petrochemical industry.”

Butanol is a relatively short molecule, with a backbone of just four carbon atoms. Molecules with longer carbon chains have been even more troublesome for biotech producers to make, particularly molecules with chains of 10 or more carbon atoms.

That’s partly because researchers have focused on ramping up the natural metabolic processes that cells use to build long-chain fatty acids. Gonzalez took a completely different approach.

“Rather than going with the process nature uses to build fatty acids, we  reversed the process that it uses to break them apart,” Gonzalez says.

“It’s definitely unconventional, but it makes sense because the routes nature has selected to build fatty acids are very inefficient compared with the reversal of the route it uses to break them apart.”

The beta oxidation process is one of biology’s most fundamental, Gonzalez says. Species ranging from single-celled bacteria to human beings use beta oxidation to break down fatty acids and generate energy.

In the new study, Gonzalez’s team reversed the beta oxidation cycle by selectively manipulating about a dozen genes in the bacteria Escherichia coli.

They also showed that selective manipulations of particular genes could be used to produce fatty acids of particular lengths, including long-chain molecules like stearic acid and palmitic acid, which have chains of more than a dozen carbon atoms.

“This is not a one-trick pony. We can make many kinds of specialized molecules for many different markets. We can also do this in any organism,” Gonzalez says.

“Some producers prefer to use industrial organisms other than E. coli, like algae or yeast. That’s another advantage of using reverse-beta oxidation, because the pathway is present in almost every organism.”

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