As you read this, I’ve got a bunch of yeast in my basement making me very happy. Over the next couple of days, they’ll happily eat up all of the simple sugars extracted from malted barley in the wort I prepared on Saturday and leave behind alcohol for what hopefully will be a very tasty brew. While people have been using yeast to make alcohol for thousands of years, it is only recently that we started using them for another purpose altogether.
Well, sort of.
As people become more and more concerned about finding alternative fuels to gasoline, they turn more and more to plants and animals. Ethanol fuel production for transpiration, for example, tripled worldwide between 2000 and 2007. Most gases in the U.S. today use some sort of gasoline/ethanol blend.
And believe it or not, this ethanol is actually the exact same alcohol you guzzle every time you tip back a cold one. Thus, it’s made in mostly the same way; using common strains of yeast to ferment sugars into alcohol.
Here’s the catch; it’s wildly inefficient for commercial means. In a perfect world, the yeast would get a hold of a bunch of biomass – wood chips, pulp, corn, grass and what not – and convert all of its sugar into ethanol. By comparison, beer is made by extracting all of the simple sugars from the grain while leaving behind the more complex sugar molecules like xylose, which specifically makes up about 30 percent of all plant matter.
So while biomass can be converted to biofuel, there’s still at least 30 percent of the original fermentable mass that goes to waste, making the whole process inefficient and too costly for wide commercial use.
Bark beetles live off of wood, which has a large amount of xylose and other typically unfermentable sugars. In order to get their energy and nutrients from the tough substances, they’ve evolved to form a symbiotic relationship with a few types of fungus. The beetles dig holes in the wood, plant the fungus spores, let it grow and decompose the wood, and reap the benefits.
In order to try to get common yeast strains to take on this rare ability, Wohlbach used comparative genetics. She looked at the DNA of the wood-eating fungus – as well as some other xylose-eating critters – and compared it to typical strands of yeast used for the production of biofuel. After isolating several genes that were active in the fungi but not in the yeast, Wohlbach turned them on in the yeast to see if it would help them eat xylose.
Sure enough, several of the genes helped the yeast convert xylose into ethanol, especially one named CtAKR. With more improvements such as this, biomass conversion to ethanol will become more and more efficient, hopefully eventually becoming a truly viable alternative fuel source.