Bacteria: The oldest form of life.

It is now believed that bacteria may have existed over three billion years ago. Most scientists believe bacteria were the first living cells on earth. Until recently there was very little evidence to support this. Bacteria are very small, and their bodies are soft. They leave very little evidence behind after they die. No one believed that fossil remains of bacteria could be found. But scientists studying ancient rocks with electron microscopes have found fossil bacteria. The fossils are more than three billion years ago. It is believed that these ancient forms of life must have lived without oxygen. They may have obtained energy through chemical reactions with iron, sulfur, or nitrogen. Some bacteria today do this every thing. The word’s great deposits of iron ore may be a result of bacterial action.

When algae and green plants became plentiful, great amounts of oxygen were thought to have been produced. The bacteria adjusted well to this change. Today bacteria are found everywhere life can exist. Bacteria are found in air, water, soil, your food, your bodies, and in the bodies of all living organisms. Although bacteria are probably the oldest living forms of life, they are considered the simplest of cells. They are called prokaryotes. This means they do not have an organized nucleus. For this reason, bacteria and blue-green algae are often classified in the kingdom Prokaryotae.

In any science, a few named stand out above all others. In biology, one such name is Louis Pasteur. Among other things, Pasteur developed a vaccine for rabies and defeated the theory of spontaneous generation. Even if he had done nothing else, he would still be remembered for these achievements. However, they represent only a small part of his work. Pasteur actually began his scientific career as a chemist. In 1854 he was appointed professor of chemistry and dean at the University of Lille. This location was quite important. The city of Lille was a center for making alcohol by fermenting the juice of sugar beets. A serious problem arose with the juice in several vats. It began to turn sour instead of changing to alcohol. Pasteur was called in to find out what was wrong. Pasteur studied the juice that was fermenting normally. Through his microscope he saw many yeast cells spread through the liquid. Over several hours, more yeast cells grew. As they grew, the alcohol content of the juice rose.

Were the yeasts producing the alcohol? In trying to learn the answer, Pasteur next examined the sour juice. This juice contained lactic acid, not alcohol. Microscopic observation showed the fermented juice contained smaller, rod-shaped bodies instead of the usual yeasts. These bodies moved and seemed to be alive; they increased in number just as the yeasts had done before. But as these rod-shaped bodies increased, the lactic acid content of the juice also increased. These discoveries led Pasteur to begin a much more complete study of fermentation. After three years he set up a small laboratory in Paris. There he finally proved his theory. Fermentation results from the action of microorganisms, and the products formed depend on the organisms involved. Yeasts produce alcohol. Lactic acid is formed by bacteria. This was only one of many discoveries by Pasteur. He lived and worked in a time of ignorance and fear of science. His discovery of a vaccine against anthrax, a disease that killed cattle and sheep, created a great deal of interest. Other scientists felt encouraged to investigate disease and immunity. Pasteur’s work helped change people’s attitude toward science. His influence affects you in many ways today. The milk you drink, for example, is pasteurized. This process of heating milk to prevent the growth of bacteria was developed by Pasteur.

Many people think of bacteria only as disease-causing organisms. But most bacteria are not harmful. Bacteria are necessary in production of certain foods and in the decay of dead organisms. Some bacteria are beneficial and necessary for proper function of our bodies. Some are necessary for the production of foods, especially dairy products. Buttermilk, cottage, cheese, yogurt, and cream cheese production all utilize bacteria that produce lactic acid. Production of hard cheese like “cheddar” may involve the use of more than one type of bacterium. Some chesses like “Roquefort” are produced using the action of bacteria and molds. Vinegar is another product in which bacteria are used.

Organisms are decomposed after death and their materials are returned to the earth and atmosphere. Did you know that bacteria are largely responsible for decomposition? During decay, bacteria break down complex molecules in dead plant and animal matter and form simpler chemical compounds. Bacteria do this in order to get food and energy. The matter that once composed a living organism is broken down by bacteria into substances that can then be used by other living things. The materials, therefore, can be used over and over again. The process of recycling matter is essential to life. If matter were “looked up” as complex molecules in dead organisms, soon there would not be enough raw material to support life. Bacteria are essential in this recycling process.

About 2.000 different species of bacteria have been identified. There are many more that are not classified. Identification of bacteria can be very important. If, for example, there is an outbreak of a deadly type of blood poisoning, the source of that disease must be found to prevent further spread of disease. The basic shapes of bacteria and the forms they assume in colonies are as follows:

- Coccus: sphere-shaped cells.

diplococcus: cells often joined in pairs or short filaments.

staphylococcus: clusters of cells.

streptococcus: chains of cells.

tetrad: four cells arranged in a square.

- Bacillus: rod-shaped cells.

diplobacillus: cells in pairs.

streptobacillus: cells joined end to end, forming a filament.

- Spirillum: cells shaped like bent rods or corkscrews.

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Compared to a virus, a bacterium is large. A single bacterium can contain 300 phage viruses. Bacteria are measured in micrometers, sometimes referred to as microns. One micrometer equals one thousandth of a millimeter. A typical sphere-shaped bacterium is one micrometer in diameter. It would lake well over one thousand of them to stretch across the inside of the letter ‘o’. The smallest bacteria are rickettsia. They cause a variety of infections. They are transmitted by arthropods (insects, spiders, and so on). These are disease-causing bacteria that are from 3 to 5 micrometers in diameter. They can barely be seen with the light microscope. The general shape of bacteria can usually be seen under the light microscope, but little of their structure can be identified. Bacteria are stained with special dyes in order to see some of their structures more clearly. Special lenses, such as oil-immersion lens, can be used to increase magnification to 1000X. With this lens more details of a bacterium can be seen.

Date: 2015-12-18; view: 806