Environmental and Nutritive Adaptations

Most bacteria may be placed into one of three groups based on their response to gaseous oxygen. Aerobic bacteria thrive in the presence of oxygen and require it for their continued growth and existence. Other bacteria are Anaerobic, and cannot tolerate gaseous oxygen, such as those bacteria that live in deep underwater sediments, and those that cause bacterial food poisoning. The third group is the Facultative anaerobes, which prefer growing in the presence of oxygen, but can continue to grow without it. Bacteria may also be classified both by the mode by which they obtain their energy. Classified by the source of their energy, bacteria fall into two categories: Heterotrophs and Autotrophs. Heterotrophs derive energy from breaking down complex organic compounds that they must take in from the environment, which includes bacteria found in decaying material, as well as those that rely on fermentation or respiration. The other group, the Autotrophs, fixes carbon dioxide to make their own food source; which may be fueled by light energy (photoautotrophic), or by oxidation of nitrogen, sulfur, or other elements (chemoautotrophic). While chemoautotrophs are rare, photoautotrophs are common and quite diverse. They include green sulfur bacteria, purple sulfur bacteria, and purple non-sulfur bacteria. The sulfur bacteria are particularly interesting, since they use hydrogen sulfide as hydrogen donor, instead of water like most other photosynthetic organisms. They are particularly useful in remediation of agricultural and residential sanitation applications, where sulfur needs to be fixed and removed in order to control noxious odors.