The Archaea Clan

Archaea are not bacteria and can be organized into subgroups. Microbiologists use one of two subgroup classifications for archaea. One classification method divides archaea into five subgroups. These are:

• Methanogenic archaea. A single-celled archaea that produces methane and carbon dioxide (CO2) through the fermentation of simple organic carbon compounds or the oxidation of H2 without oxygen to produce CO2.

• Sulfate reducers. Archaea that function in the presence of air.

• Extreme halophiles. Archaea that live in an extremely salty environment.

• Cell wall-less archaea. Archaea that do not have a cell wall.

• Extremely thermophilic S-metabolizers. Archaea that need sulfur for growth.

The other method used to organize archaea into subgroups is used in Bergey's Manual of Systematic Bacteriology that you learned about in Chapter 9; it consists of two branches (phyla). These are:

• Phylum crenarchaeota. Archaea that are within the phylum crenarchaeota branch are anaerobes (they live in the absence of oxygen) and grow in a sulfur-enriched soil or water environment that is at a temperature between 88 and 100 degrees Fahrenheit and has a pH between 0 and 5.5. Extremely thermophilic S-metabolizers are within the phylum crenarchaeota subgroup.

• Phylum euryarchaeota. The phylum euryarchaeota branch consists of the following five major groups:

• Methogenic archaea. Methogenic archaea, the largest group of phylum euryarchaeota, are anaerobic archaea that synthesize organic compounds in a process called methanogenesis, which produces methane. They also use inorganic sources (autotrophic) such as H2 and CO2 for growth. Methogenic archaea thrive in swamps, hot springs, and fresh water as well as in marshes. They digest sludge and transform undigested food, in animal intestines and in the rumen of a ruminant, into methane. A ruminant is a herbivoir that has a stomachs which is divided into four compartments. The rumen is the expanded upper compartment of the stomach that contains regurgitated and partially digested food called a cud. Methogenic archaea transform regurgitated and partially digested food into methane (CH4), which is a clean-burning fuel. For example, a cow can belch up to 400 liters of methane a day. Sewage treatment plants also use methogenic archaea to transform organic waste into methane. Although methane is a source of energy, it is also a cause for the greenhouse effect. Methogenic archaea are further organized into five orders. These are: methanobacterioles, methanococcales, methanomicrobiales, methanosareinales, and methanopyrales.

• Extreme halophiles. Extreme halophiles, also known as halobacteria, absorb nutrients from dead organic matter absorb nutrients in the presents of oxygen (aerobic chemoheterotrophs). They require proteins, amino acids, and other nutrients for growth in a high concentration of sodium chloride. Extreme halophiles can be motile or nonmotile and are found in salt lakes and in salted fish and turn lakes and fish red when there is an abundance of Extreme halophiles.

• Halobacterium salinarium. Halobacterium salinarium is an archaea that acquires energy through photosynthesis. However, it is able to do so without the need of chlorophyll or bacteriochlorophyll. Halobacterium sali-narium synthesizes the bacteriorhodopsin protein,which shows as a deep purple color under high-intensity lighting in a low-oxygen environment.

• Thermophilic archaeon. Thermophilic archaeons are known as thermoplasma and grow in hot (55 to 59 degrees Celsius), acidic (pH of 1 to 2) refuse piles of coalmines that contain iron pyrite. These refuse piles become hot and acidic as chemolithotropic bacteria oxidize iron pyrite into sulfuric acid. Thermophilic archaeons lack a cell wall.

• Sulfate-reducing archaea. Sulfate-reducing archaea are known as archaeoglobi and extract electrons from various donors to reduce sulfur to sulfide in an environment that is approximately 83 degrees Celsius such as near marine hydrothermal vents (underwater hot springs). Sulfate-reducing archaea are gram-negative and are shaped as irregular spheres (coccoid cells).

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