July 2011

Pouring energy into biofuels

“I strongly believe that modification of these specific cofactors will provide us with the global key for conversion of starch to oil in any organism,” she says. In principle, she adds, there’s no need to switch starch for oil in seeds. Rather, genetic engineering could put the activity of these key cofactors in a plant’s vegetative tissues, or even in algae or bacteria, changing their metabolisms to spit out more oil.

James Liao, chancellor’s professor and vice-chairman of the department of chemical and biomolecular engineering at the University of California, Los Angeles, also is working on moving away from ethanol by using synthetic biology to engineer bacteria that churn out longer-chain alcohols with significantly higher energy density.

James Liao of the University of California, Los Angeles has engineered photosynthetic cyanobacteria that produce a variety of higher alcohols. Photo credit: Yixin Huo and Xiaoqian Li.

Using E. coli as their model organism, Liao and his colleagues leaned on this organism’s native amino acid biosynthesis pathways pathways to create starter molecules for various alcohols. They then strung together genes from various other organisms, including Sacchromyces, Lactococcus and Clostridium, for enzymes to convert these molecules into the desired product. Using this method, the researchers engineered E. coli that produced a variety of higher alcohols, including isobutanol, 1-butanol, 3-methyl-1-butanol, and 2-methyl-1-butanol, from glucose.

Not ones to rest on their laurels, Liao’s team followed this research up with another paper, published the next year, that used parts of the same pathway in photosynthetic cyanobacteria. The resulting organism produces isobutyraldehyde and isobutanol by pulling carbon directly from carbon dioxide in air.

In a recent paper, Liao’s lab detailed their synthesis of E. coli that produce alcohols from protein – thus far, an unutilized feedstock – by redirecting this organism’s metabolic flow of nitrogen.

“We like to keep pushing things further and further,” he says.

Jay Keasling, a professor in the departments of chemical and biomolecular engineering and bioengineering at the University of California, Berkeley, also is harnessing the power of synthetic biology for biofuels, both higher-chain alcohols and biodiesel from fatty acids.

In one recent paper, Keasling and his colleagues engineered yeast that make n-butanol, a far cry from the ethanol this organism usually makes. Rather than rely on the amino acid biosynthesis pathway that Liao’s team used, the researchers instead modified the acetyl-CoA pathway using genes from five other organisms. The team mixed combinations of individual genes, eventually producing seven different modified strains. One of these successfully produced significant quantities of n-butanol. This year, Keasling’s former postdoctoral fellow Michelle Chang, now an assistant professor of chemistry at University of California, Berkeley, significantly improved these yields with some of these same non-native components in E. coli.

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