EFFECTS OF THE ENVIRONMENT ON MICROBIAL GROWTH Organisms survive and grow under optimal conditions but exactly what constitutes optimal conditions can vary with the type or organism. Some anaerobic organisms are not equipped to survive the reactive oxygen species that come out of living in a high oxygen environment. Organisms that survive in extreme locations are actually anaerobic and do not live well when oxygen is present. This can include places like sewers, the intestines, deep in the earth’s crust, bogs, and marshes do not survive well with oxygen present. Bacteria can be grown in thioglycolate tube cultures that is low in oxygen. The organism is stabbed into the tube and can become motile within it. It gradually picks up oxygen from the top of the tube on down. The maximum growth occurs at the level where the oxygen concentration is optimal. Organisms at the top are obligate aerobes, while organisms at the bottom are obligate anaerobes. Organisms that grow throughout are called facultative anaerobes but they will concentrate at the top. Aerotolerant anaerobes will growth throughout. Microaerophiles grow somewhere in between, where oxygen content is lower than atmospheric oxygen levels. Obligate anaerobes are difficult to grow. They need to be grown in an anaerobic jar, which chemically removes the oxygen, or in anaerobic chambers, which are also anaerobic. Mixed bacterial infections are common in humans, which usually involve anaerobes and aerobes. Some organisms will operate somewhere between a minimum permissive oxygen concentration and a maximum permissive oxygen concentration. The process of aerobic respiration involves the making of reactive oxygen species as byproducts. These need to be detoxified from the cell. There are three important enzymes that do this: catalase, peroxidase, and superoxide dismutase. Each does a slightly different thing to detoxify reactive oxygen species. Obligate anaerobes will not have any of these enzymes, while other organisms will have just one or two of these. Some organs are called capnophiles because they like high carbon dioxide levels and low oxygen levels. They can grow in candle jars in which a candle has been lit to get rid of oxygen and release carbon dioxide as a byproduct of the burning process.
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