Chapter 27: Environmental Microbiology

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.