University of Illinois
scientists have engineered a new strain of yeast that converts seaweed into
biofuel in half the time it took just months ago. That’s a process that’s important
outside the Corn Belt, says Yong-Su Jin, a University of Illinois
assistant professor of microbial genomics and a faculty member in its Institute
for Genomic Biology.
“The key is the strain’s
ability to ferment cellobiose and galactose simultaneously, which makes the
process much more efficient,” Jin says.
Red seaweed, hydrolyzed for its
fermentable sugars, yields glucose and galactose. But yeast prefers glucose and
won’t consume galactose until glucose is gone, which adds considerable time to
the process, he says.
The new procedure hydrolyzes
cellulose into cellobiose, a dimeric form of glucose, then exploits a newly
engineered strain of Saccharomyces
cerevisiae capable of fermenting cellobiose and galactose simultaneously.
The team introduced a new sugar
transporter and enzyme that breaks down cellobiose at the intracellular level.
The result is a yeast that consumes cellobiose and galactose in equal amounts
at the same time, cutting the production time of biofuel from marine biomass in
half, he says.
The research, performed with
project funding from the Energy Biosciences Institute, included team members
Suk-Jin Ha, Qiaosi Wei, and Soo Rin Kim of the University of Illinois,
Urbana-Champaign, and Jonathan M. Galazka and Jamie Cate of the University of
California, Berkeley.
Jin compared the previous process
to a person taking first a bite of a cheeseburger, then a bite of pickle. The
process that uses the new strain puts the pickle in the cheeseburger sandwich
so both foods are consumed at the same time.
Co-fermenting the two sugars also
makes for a healthier yeast cell, he says.
“It’s a faster, superior
process. Our view is that this discovery greatly enhances the economic
viability of marine biofuels and gives us a better product,” he adds.
Is seaweed a viable biofuel? Jin
and his colleagues are using a red variety (Gelidium
amansii) that is abundant on the coastlines of Southeast
Asia. In island or peninsular nations that don’t have room to grow
other biofuel crops, using seaweed as a source of biofuels just makes good
sense, he noted.
But biofuels made from marine biomass
also have some advantages over fuels made from other biomass crops, he says.
“Producers of terrestrial
biofuels have had difficulty breaking down recalcitrant fibers and extracting
fermentable sugars. The harsh pretreatment processes used to release the sugars
also result in toxic byproducts, inhibiting subsequent microbial
fermentation,” he says.
Jin cited two other reasons for use
of seaweed biofuels. Production yields of marine plant biomass per unit area
are much higher than those of terrestrial biomass. And rate of carbon dioxide
fixation is much higher in marine biomass, making it an appealing option for
sequestration and recycling of carbon dioxide.
