There are nearly eight cars for every 10 people in the United States today. The high demand for gasoline requires more than 9 million barrels of oil per day. Not only does this consumption increase the country's dependence on foreign oil, but it also stresses the environment. One alternative to gasoline is ethanol, a fuel made from the fermentation and distillation of sugars and starches. While ethanol has been made from sugarcane, in the U.S. it's usually made from corn, which is a more abundant crop.

Ethanol is oxygen-rich, so it burns relatively cleanly. By adding it to gasoline, it reduces the amount of gasoline consumed. This in turn reduces the amount of harmful gases that enter the atmosphere and can cause air and water pollution, global warming, and smog. Yet despite these stated environmental benefits, ethanol made from corn kernels has become a controversial subject. Critics believe that widespread production of ethanol will result in more land being used to grow corn for fuel rather than for food. They also believe that producing and using ethanol actually does more harm to the environment than good. According to some calculations, producing corn and processing it into one gallon (3.7 liters) of ethanol requires more energy than that gallon of ethanol contains.

A newer and possibly less controversial approach to biofuels is to use cellulosic ethanol, which is made from cellulosic biomass. The term cellulosic biomass refers to nonfood, plant-based material, such as corn stalks, wood chips, and switch grass. While making fuel from cellulosic biomass has the potential to be more sustainable than corn kernel ethanol, it's currently more expensive to produce. Turning biomass into ethanol is a two-step process. First, enzymes must be employed to break the more complex cellulose into simple sugars. Then, yeast must be added to ferment the sugar into ethanol.

Genetically modified bacteria, like those discussed in this video segment, could enhance the efficiency and reduce the cost of cellulosic ethanol production by simplifying the two-step process into one. The bacteria are capable of both breaking down the biomass and fermenting the sugar. Further, because the microbes are thermophilic (heat-loving) and grow at temperatures of 50°C to 60°C, they could produce ethanol at higher temperatures than yeast: this reduces the quantity of costly enzymes needed to split the cellulose into sugars that the microbes can ferment. Still, even with this emerging technology, ethanol will probably never replace gasoline in the volume that Americans consume at present.

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