— Scientists who engineer microbes to efficiently produce biofuels from plants and algae are busy reporting breakthroughs that could wean us from fossil fuels — offering a glimmer of hope to consumers eyeing gas prices skyrocket.
In one breakthrough, a microbe has been genetically engineered to produce isobutanol, a gasoline-like fuel, directly from cellulose.
"That's the first time cellulose has directly been used to produce four-carbon alcohols," James Liao
, vice chair of chemical and biomolecluar engineering at the University of California, Los Angeles, told me today.
Cellulose such as switchgrass and the leaves and stalks of corn, is a more abundant and cheaper feedstock for biofuel production than corn and sugarcane, but is difficult to breakdown to the sugars that microbes convert into alcohol fuels.
For example, some strains of the microbe Clostridium produce butanol, but they don't do so directly from cellulose. It first has to be broken down into sugars. Other species of Clostridium digest cellulose, but don't produce butanol, Liao explained.
"We designed a new pathway" that allows Colstridium to produce isobutanol directly from cellulose and transferred that pathway into the Clostridium celluloyticum, Liao said. This strain naturally digests cellulose. Their genetic manipulation allows it to produce isobutanol as well.
In addition, isobutanol is a higher grade of alcohol than ethanol, which is primarily produced today from corn. Most cars on the road can run on blends of gasoline with up to 10 percent ethanol.
"Unlike ethanol, isobutanol can be blended at any ratio of gasoline and should eliminate the need for dedicated infrastructure in tanks or vehicles," Liao added in a press release
about the breakthrough. "Plus, it may be possible to use isobutanol directly in current engines without modification."
The research was published online in the journal Applied and Environmemental Microbiology
The promise of butanol as a biofuel is spurring several researchers to genetically optimize microbes to produce it. Researchers at the University of California at Berkeley reported March 2 a genetically engineered strain of E. coli that produces n-butanol
at rate that is 10 times better than competing systems.
The researchers are interested in using E. coli, which doesn't naturally produce butanol, because it is easier to work with and scale up the process for industrial production of biofuel.
Unlike the new microbe, however, the E. coli currently uses straight sugar to produce the fuel. More research will be required to figure out how to get the sugar from biomass, Michelle Chang, the Berkeley chemist leading the research effort, told me.
Liao's group at UCLA is also at work on engineering E. coli to produce n-butanol and have achieved 15 to grams per liter from sugar. Their paper will be published online later this week.
Fuel from proteins
In addition, Liao's team published research on Sunday in the journal Nature Biotechnology
describing a method for producing biofuels where "we use proteins instead of cellulose, sugars, or lipids," he told me.
To do this, the team changed the metabolic pathways in E. coli so that they efficiently remove nitrogen from groups of amino acids — the building blocks of proteins — to produce alcohols, which are converted to biofuels.
The team argues that proteins are attractive molecules to turn into fuels because proteins are produced as byproducts from current industrial processes and because they can be made more abundant than carbohydrates from sugars and cellulose and lipids from vegetable oil.
Until now, however, no one knew how to turn them into fuel.
"Microorganisms tend to use proteins to build their own proteins instead of converting them to other compounds," Yi-xin Huo, a UCLA postdoctoral researcher and lead author of the study, said in a news release
Liao's team created an artificial metabolic system to dump reduced nitrogen out of cells and tricked the cells to degrade proteins without utilizing them for growth. Proteins contain both ammonia and carbon; Liao's team took away the ammonia and recycled it back for the growth of the algae they worked with.
"Today, nitrogen fertilizers used in agriculture and biofuel production have become a major threat to many of the world's ecosystems, and the nitrogen-containing residuals in biofuel production can eventually turn into nitrous oxide, which is about 300 times worse than CO2 as a greenhouse gas," Liao added in the news release.
"Our strategy effectively recycles nitrogen back to the biofuel production process, thus approaching nitrogen neutrality."
The researchers are now working on scaling up the technology.