For many people, the words germ and microbe bring to mind a group of tiny creatures that do not quite fit into any of the categories in that old question, “Is it animal, vegetable, or mineral?”
Microbes, also called microorganisms, are minute living things that individually are usually too small to be seen with the naked eye. The group includes bacteria, fungi (yeasts and molds), protozoa, and microscopic algae. It also includes viruses, those noncellular entities sometimes regarded asst raddling the border between life and nonlife.
We tend to associate these small organisms only with major diseases such as AIDS, uncomfortable infections, or such common inconveniences as spoiled food. However, the majority of microorganisms make crucial contributions by helping to maintain the balance of living organisms and chemicals in our environment.
Marine and freshwater microorganisms form the basis of the food chain in oceans, lakes, and rivers. Soil microbes help break down wastes and incorporate nitrogen gas from the air into organic compounds, thereby recycling chemical elements between the soil, water, life, and air. Certain microbes play important roles in photosynthesis, a food- and oxygen-generating process that is critical to life on Earth.
Humans and many other animals depend on the microbes in their intestines for digestion and the synthesis of some vitamins that their bodies require, including some B vitamins for metabolism and vitamin K for blood clotting.
Microorganisms also have many commercial applications. They are used in the synthesis of such chemical products as vitamins, organic acids, enzymes, alcohols, and many drugs. The process by which microbes produce acetone and butanol was discovered in 1914 by Chaim Weizmann, a Russian-born chemist working in England.
With the outbreak of World War-I in August of that year, the production of acetone became very important for making cordite (a smokeless form of gunpowder used in munitions). Weizmann’s discovery played a significant role in determining the outcome of the war.
The food industry also uses microbes in producing vinegar, sauerkraut, pickles, alcoholic beverages, green olives, soy sauce, buttermilk, cheese, yogurt, and bread. In addition, enzymes from microbes can now be manipulated to cause the microbes to produce substances they normally do not synthesize. These substances include cellulose, digestive aids, and drain cleaner, plus important therapeutic substances such as insulin. Microbial enzymes may even have helped produce your favorite pair of jeans.
Though only a minority of microorganisms are pathogenic (disease-producing), practical knowledge of microbes is necessary for medicine and the related health sciences. For example, hospital workers must be able to protect patients from common microbes that are normally harmless but pose a threat to the sick and injured.
Today we understand that microorganisms are found almost everywhere. Yet not long ago, before the invention of the microscope, microbes were unknown to scientists. Thousands of people died in devastating epidemics, the causes of which were not understood. Entire families died because vaccinations and antibiotics were not available to fight infections.
We can get an idea of how our current concepts of microbiology developed by looking at a few historic milestones in microbiology that have changed our lives.