“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
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,
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.