We humans can be a rather arrogant lot. For thousands of years, we've been claiming that we have been making beer and wine. The truth is that the alcohol in beer and wine (and all other alcoholic drinks, for that matter) is made by yeast, a much less arrogant animal. All you need to do is feed yeast some sugar or starch, it will make alcohol by fermentation, and it will so so quickly and efficiently.
The good news is, you can also use that alcohol for fuel. The bad news is, humans eat sugar and starch for food just like yeast do. Which means that as it stands now, renewable ethanol fuel directly competes with food for cropland.
What we need is a way to produce ethanol from renewable crops that we can't eat, and that don't compete with farmland.
Crops like trees, for example, or switchgrass, which can grow on land unsuitable for crops. But to do that, we need to find a way to make ethanol out of complex carbohydrates like cellulose and lignin. This idea is called "cellulosic ethanol," and so far, we don't have a cheap way to do it.
Until now, most research into cellulosic ethanol has focused on chemical processes that can break down cellulose into simple sugars, a process called hydrolysis. With the right kind of enzyme or the right process, you can convert the cellulose to sugar, and then feed the sugar to yeast, which do their fermentation trick.
Attempts to use biological processes to turn cellulose into ethanol have been less successful, because until now the only critters that could break down cellulose are certain bacteria, and they're not too fast or efficient at doing that. Which is a good thing, because if they were, we wouldn't be able to build any long lasting structures out of wood.
Bacteria break down cellulose using a "cellulosome" (also called a scaffoldin), which is a suite of enzymes on their outer surfaces that break down cellulose.
Recently, scientists at the University of California Riverside announced that they had created an artificial cellulosome on the surface of yeast cells, using mix-and-match components from several species of bacteria.
And when they fed these engineered yeast a diet of cellulose, they got ethanol -- a lot of it. In fact, they got about 95% of the theoretical maximum they could have gotten from the cellulose. All in one easy step.
I should point out that the remaining problems are large. The artificial cellulosome currently has to be manufactured, which isn't necessarily easy. Perhaps someday the yeast's own genome might be engineered to create the necessary enzymes.
But that won't be easy either: enzymes of this type, called cellulases, contain two major pieces, a dockerin domain and a glucanase domain. Each of the three enzymes used by the UCR scientists used a dockerin from one place and a glucanase from another place. In other words, none of these enzymes actually exists in nature as a complete whole. So there is a lot of work yet to do.
But yes. This could be very big.
Science News article here.
Peer-reviewed abstract here.