Microorganisms surround us on all sides and make their presence felt throughout our lives. The useful species outnumber the harmful ones by thousands to one and are so valuable that life as we know it would be impossible without them. Microorganisms break down the remains of all that die and recycle such elements as carbon, nitrogen, and sulfur; they produce numerous foods, including cheeses, dairy products, and fermented beverages; they are essential decomposers in sewage treatment; and they manufacture numerous industrial products such as drugs, insecticides, hormones, and enzymes