Single-cell organisms (also known as microorganisms) are everywhere; there are more than we can imagine just living in our own body. However, while some microorganisms are a possible risk to our health, there many practical advantages for using them in industry. Additionally, our bodies have naturally evolved to take advantage of some microorganisms.
Food and Drink Processing
Microorganisms are essential in the process known as "fermentation," which is the conversion of carbohydrates into an alcohol or a sugar. Fermentation is used to create a wide variety of food and drinks, including beer, wine, dairy products, pickles and coffee. Microorganisms, such as yeast or bacteria, are what accomplish fermentation because they cause the carbohydrate to break down when they eat or absorb it for food; this breakdown also releases energy, which is also essential to the process of fermentation.
Microorganisms also play a practical role in sewage treatment because several types of microorganisms naturally eat pathogens in human waste, and thus help purify the water. Thus, microorganisms are part of the reason why it is acceptable to dump a regulated amount of sewage water into bodies of water because natural water contains microorganisms that will help purify the waste. Microorganisms are also used to help treat water that is not dumped back into a river or stream; the second phase of sewage treatment (after solids are removed) is normally to add pathogen-eating microorganisms to the waste water.
Oil Spill Technology
Recent advancements in microbiology have shown that microorganisms may be useful in helping clean up oil spills. A study by Rebecca S. Bryant of the National Institute for Petroleum and Energy Research showed that microorganisms can be used in a couple of distinct ways to help with oil spills, including being able to produce chemicals on the surface of the oil that help break it down, and also by trapping oil in small reservoirs so that the spill is easily contained.
In addition to the innovative ways that human beings have thought to use single-cell organisms, evolution has naturally created some microorganisms that are advantageous to our health. Indeed, microorganisms in our digestive system (including the Bacteroides thetaiotaomicron) are essential to our health, as they help break down complex carbohydrates into easier-to-use sugars, much like in the process of fermentation. Additionally, other microorganisms in our body (such as Methanobrevibacter smithii) aid in helping remove waste products.