BacteriaBacteria are the most common and ancient microorganisms on earth. Most bacteria are microscopic and measure 1 micron in length. However, colonies of bacteria grown in a laboratory Petri dish can be seen with the naked eye. There are many divisions and classifications of bacteria that help identify them. The first two types of bacteria are archaebacteria and eubacteria. Both groups have common ancestors dating back more than 3 billion years. Archaebacteria live in environments where, due to the high temperature, no other life forms can develop. These environments include hot springs and areas of volcanic activity. They contain lipids but lack some chemicals in the cell wall. Eubacteria are all other bacteria. Most of them are phototrophic, that is, they use the sun's energy as food through the process of photosynthesis. Another classification of bacteria is based on their need for oxygen to live. Those who require oxygen to live are considered aerobes. Bacteria that do not use oxygen to live are called anaerobes. The specific shape of the bacteria provides the next step in the identification process. The spherical bacteria are called cocci; bacteria that have a rod shape are called bacilli; corkscrew-shaped bacteria are spirilla; and filamentous is the term for thread-like bacteria. Hans Christian Joachim Gram, a Danish microbiologist, developed a method to distinguish bacteria by their different reaction to a stain. The process of applying Gram stain is as follows: bacteria are stained with a purple dye and treated with Gram's solution (1 part iodine, 2 parts potassium iodide and 300 parts water). Ethyl alcohol is then applied to the soil; the bacteria will retain the blue color of the original dye or will obtain a red hue. Blue-colored bacteria are Gram-positive; red bacteria are identified as gram-negative. Bacteria contain DNA (deoxyribonucleic acid) just like all cells. However, in bacteria the DNA is arranged in a circular fashion rather than in strands. Bacteria also contain ribosomes which, as in eukaryotic cells, provide protein synthesis. For a bacterium to attach itself to a surface, it requires the help of pili, or hair-like growths. Bacteria, just like sperm, have flagella that aid in movement. But sperm have only one flagellum, while bacteria contain flagella at several locations on the body surface.