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What are heterotrophs and autotrophs?

All bacteria require carbon, nitrogen, sulfur, phosphorus, inorganic salts, and micronutri-ents. Bacteria that use an organic compound as their source of carbon are called heterotrophs, while those that use an inorganic source are called autotrophs. In addition, some bacteria use photosynthesis to generate energy in the form of the compound ATP; these are called phototrophs. Some species of bacteria are parasitic and can grow only within a living host cell; examples include the genera Rickettsia and Chlamydia, both of which are parasites in eukaryotic cells. Those bacteria that require oxygen, such as Bacillus, are called aerobes; anaerobes, such as Clostridium, can not survive in the presence of oxygen.

What types of bacteria do you know?

Various types of bacteria that are present in water can cause disease in humans, and water-purification plants are designed to destroy these microorganisms. Bacteria from industrial wastes may also act as pathogens, or agents of disease. Conversely, some types of bacteria act as cleansing agents in water, and water-treatment facilities utilize some such bacteria to break down the organic matter that is present in sewage.

Various types of bacteria contaminate foods and can cause food poisoning in humans. Pasteurization is routinely used to neutralize bacteria that may be present in milk, for example. Other sterilization techniques include high temperature, radiation, ethylene oxide, and other antiseptics and germicides.

What is virulence?

The ability of a bacterium to cause a disease is called virulence. One contributing factor to the degree of virulence is the type of capsule a bacterium has. Some bacteria have a specificity for various parts of the body: meningo-coccal bacteria infect the brain membranes, and tubercule bacteria infect the lungs. Some are slightly more generalized: staphylococcal bacteria can infect the skin, causing boils; the bloodstream, causing blood poisoning; and the bones, causing the condition known as osteomyelitis.

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