It’s not so long ago that corn-based ethanol was being widely touted as a nearly ideal form of alternative energy. It was liquid, so it could be used for a transportation fuel. It came from plants, so the carbon dioxide it emitted during burning was at least partly offset by the carbon dioxide it absorbed while the corn was growing. And it was domestic — no need to deal with unstable or unfriendly regimes across the sea.
The bloom has faded from corn ethanol, though, mainly because it turns out to be less kind to the atmosphere than you might think. In large part, this is because plowing and harvesting take lots of energy. So does the manufacture of fertilizer you need to grow the corn, and so does the plant that processes the corn into ethanol. Even if you calculate it generously, only about two of every ten gallons of ethanol actually represent renewable energy.
That’s not the case with cellulosic ethanol — that is, ethanol made from woody plants, cornstalks, wood chips and other fibrous plant matter, which in many cases are simply the byproducts of agriculture. But there’s a catch there too: ethanol is harder and more expensive to make from these materials than it is from corn.
But a paper just published in Plant Biotechnology Journal may point the way to a solution — and offer an important, unrelated benefit as well. A team of scientists at the University of Central Florida has engineered tobacco plants to churn out enzymes normally produced by fungi. Enzymes are crucial to breaking cellulose down into a fermentable form, but they’re prohibitively expensive to use at commercial scale. “The cost of these enzymes,” says molecular biologist Henry Daniell, a co-author of the study, “has been the greatest barrier.”
To overcome that barrier, Daniell and his colleagues found a way to snip enzyme-producing genes from fungi and insert up to 10,000 copies of them into the genomes of tobacco plants — which are much easier to grow than fungi and can in principle produce several crops of enzyme-rich plants every year. As a result, says the report, the cost of key enzymes (which is, of course, not the only cost in making cellulosic ethanol) can be more than 1,000, and in some cases more than 3,000, times lower than the cost of comparable enzymes made from fungi. “There are perhaps 8-10 core enzymes,” says Daniell, “that you need to create tailor-made ‘cocktails’ for different kinds of plant matter.”
With one mix of enzymes, they suggest, you could turn Florida’s discarded orange peels into ethanol. In the Midwest, a different enzyme cocktail could process corn stover — the stalks, leaves and other waste left over after harvesting. Yet another cocktail could turn old newspapers into ethanol.
The unrelated benefit: antismoking campaigns have put pressure on tobacco farmers to think about switching to more socially acceptable crops. But if tobacco itself could be used, not for a product promoting lung cancer and heart disease, but rather for creating a more climate-friendly fuel, the pressure might be reduced.
And there’s more potential good news for tobacco farmers and for carbon-reduction efforts as well. Just last month, researchers from the Biotechnology Foundation Laboratories of Thomas Jefferson University in Philadelphia announced in the same journal that they too had engineered the genes of tobacco plants — in this case, to produce oil that could be used as biodiesel, an entirely different sort of alternative fuel.
In both cases, of course, what seems like a promising form of alternative energy needs to be scaled up and commercialized before it can be declared a success. Not long ago, after all, corn ethanol was getting the same sort of attention that these new forms of biofuel are now receiving. But there’s no reason to think history has to repeat itself.