Many people are interested in another application of fermentation: biofuels. Biofuels are a hot topic of research these days, as people become more and more aware of rising prices and shorter supplies of oil. Trying to get cars and trucks to run on plant material instead of oil is an interesting and challenging problem.
The product people talk about when it comes to biofuels is ethanol. Ethanol is currently used as an additive to gasoline, mostly in the U.S. and in Brazil. Gasoline bought in the US is usually 10% ethanol, but some cars and trucks are equipped to deal with higher ratios of ethanol to gasoline. Read more about the economics and politics of global ethanol production here.
What is ethanol? As mentioned earlier in this module, it comes from alcohol fermentation. Usually plant material such as corn, sugar cane, or potatoes are the sugar source, and bacteria do the fermentation work. They produce ethanol through alcohol fermentation, and that ethanol is used as fuel. Pretty cool, huh?
Of course nothing is as simple as it seems. A lot of controversy exists about biofuels, because it seems wasteful to use food crops for fuel when they could be feeding people. Since the cost of food is currently increasing, the economic benefit of replacing gasoline with ethanol can be hard to see. Also, food crops, particularly corn, take a lot of input, such as fertilizer, pesticides, and the cost of transporting them. It is unclear if the economic and environmental cost of the inputs is worth the output.
Using other plant products that are not as energy-intensive or potential food sources to produce ethanol might help this problem. This is where cellulosic ethanol comes in. Cellulose is a sugar found in the cell walls of plants, but it is harder to break down than other plant parts. Technological advances have made it possible to break down cellulose and use more plant products, such as wood chips and fast growing grasses. However, the cellulosic industry has struggled to get off the ground because of funding, the need for more research, and the lack of infrastructure to support it.
Another biofuel being researched is algae biodiesel. Biodiesel is not based on ethanol, but on actual oil harvested from algae. Since that is not as clearly related to cellular respiration, we won't spend time talking about it here.
Although researchers are looking for alternatives to oil, there is still a lot of oil being transported around the globe. With oil transportation comes the occasional oil spill. When examining the effects of oil spills in the ocean on marine life, scientists have found something really awesome: there are actually bacteria that eat oil!
Well "eat" may be a bit of an exaggeration, since bacteria do not have mouths or digestive systems, per se. These bacteria metabolize the compounds in oil because they can use other molecules as electron donors and acceptors. Crude oil is made up of many compounds, and different types of bacteria make the enzymes that can break down the different compounds in oil. Scientists are also studying bacteria that live in freshwater areas contaminated by oil. Identifying and growing bacteria from these sites may help clean up water polluted by oil.
There are lots of kinds of marine bacteria that naturally break down oil (Head et al. 2006). Currently, researchers are studying how these bacteria are related, how they interact with each other and their environment, and how we can use them for cleaning up pollution.
Many types of pollution, not just oil spills, have the potential to be cleaned up by bacteria. This is called bioremediation—basically, remedying a problem with biological solution.
Interestingly enough, not all the bacteria that might help clean up pollutants eat oils, plastics and old iPods naturally. They treat these objects as special foreign substances that might be toxic, and break down or transform them to be less harmful. Bacteria have special metabolic pathways that allow them to transform oil and other substances into different compounds.