27.1 Microbial Diversity and Habitats

• Microbes that live in extreme conditions of temperature, acidity, alkalinity, or salinity are called extremophiles.

• Symbiosis is a close association between two unlike organisms that is beneficial to one or both of them.

  • An important example of symbiosis is the relationship between plant roots and certain fungi, called mycorrhizae, or mycorrhizal symbionts.

27.2 Soil Microbiology and Biochemical Cycles

• In biogeochemical cycles, elements are oxidized and reduced by microorganisms to meet their metabolic needs.

  • The primary biogeochemical cycle is the carbon cycle.

• This increased atmospheric carbon dioxide is causing global warming of the Earth.

• The nitrogen cycle is all organisms need nitrogen to synthesize protein, nucleic acids, and other nitrogen-containing compounds.

• In a process called deamination, the amino groups of amino acids are removed and converted into ammonia.

• Cyanobacteria usually carry their nitrogenase enzymes in specialized structures called heterocysts that provide anaerobic conditions for fixation.

• Rhizobia, as these bacteria are commonly known, are specially adapted to particular leguminous plant species, on which they form root nodules.

• An important contribution to the nitrogen economy of forests is made by lichens, which are a combination of fungus and an alga or a cyanobacterium in a mutualistic relationship.

• The sulfur cycle and nitrogen cycle resemble each other in the sense that they represent numerous oxidation states of these elements.

• As proteins are decomposed, in a process called dissimilation, the sulfur is released as hydrogen sulfide to reenter the cycle.

  • Such bacteria are called endoliths (inside rocks), which must grow in the near absence of oxygen and with minimal nutrient supplies.

• The phosphorus cycle instead involves changes from soluble to insoluble forms and from organic to inorganic phosphate, often in relation to pH.

  • The use of microbes to detoxify or degrade pollutants is called bioremediation.

• Composting is a process gardeners use to convert plant remains into the equivalent of natural humus.

27.3 Aquatic Microbiology and Sewage Treatment

• The limnetic zone consists of the surface of the open water area away from the shore.

• The profundal zone is the deeper water under the limnetic zone.

• The benthic zone contains the sediment at the bottom.

• The support of oceanic life depends largely on such photosynthetic microscopic life, the marine phytoplankton.

• Microbial bioluminescence, or light emission, is an interesting aspect of deep-sea life.

• These additional nutrients cause dense aquatic growths called algal blooms.

• The tests for water purity in use today are aimed instead at detecting particular indicator organisms.