Imagine inheriting a huge chunk of money, spending it carelessly for a while, then suddenly realizing you need to change your ways and live off the interest alone. Replacing fossil fuels with biofuels is pretty much the same deal. Nature has stored away millions of years' worth of biomass in coal and oil deposits, and we've gotten used to consuming a lot more of that stored energy each year than the earth can replenish.
When we consider a shift to biofuels we run up against that basic problem pretty hard: we can only squeeze just so much energy for fuel out of our global ecosystem's annual productivity, and we've gotten used to using a lot more than that.
But a new study published this week suggests that a bit of genetic tinkering can help a microorganism boost its ability to turn organic matter into usable fuel, which might make it a bit easier to run our vehicles on fuel that doesn't spend down our fossil fuel inheritance.
In the study, published January 20 in Nature Communications, a team of researchers at The University of Texas at Austin's Cockrell School of Engineering changed the genetic makeup of a strain of yeast to make it much better at turning carbohydrates into fat. The breakthrough offers the potential of efficiently converting organic matter into high-energy fuel.
The yeast, Yarrowia lipolytica, has been eyed for some time by biofuel researchers; it can produce a relatively large amount of fat as a result of digesting simple sugars. But that "relatively large" amount of fat compared to other yeasts can still use some boosting. Until recently, biofuel researchers had been able to create yeast strains whose cells contained about 50 percent fat, and they had to culture those cells carefully, starving them of nitrogen, to induce the yeast to create and store fat.
Nitrogen is an essential nutrient for yeasts: they, along with the rest of us, need it to create proteins. That means that nitrogen-starving your yeasts is not something you can do 24/7 and expect them to thrive.
The Cockrell School of Engineering's team found a way to tweak Yarrowia's genome so that the cells produce far more fat without being deprived of nitrogen. The engineered yeast strain's cells achieved fat contents of up to 90 percent, which the researchers -- led by UT Austin assistant professor Hal Alper -- converted into a fuel similar to soy-based biodiesel.
"We took a starting yeast strain of Yarrowia lipolytica, and we've been able to convert it into a factory for oil directly from sugar," Alper said in a press release. "This work opens up a new platform for a renewable energy and chemical source."
The fact that the yeast requires sugar as a fuelstock poses a potential long-term problem, given that the push for biofuels is already driving food prices higher in many parts of the world. And mistrust of genetically modified organisms among the environmentally oriented crowd may blunt enthusiasm for the breakthrough.
Still, making biofuels by fermentation is a potential step toward making our fuel more sustainable.