CRENARCHAEA

SYSTEMATIC BIOLOGY					THE ARCHAEA
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PHYLUM CRENARCHAEOTA

INTRODUCTION TO THE CRENARCHAEOTA

Crenarchaeota (kren-ar-ke-O-ta) is fromed from two Greek roots that mean "fountain" (krene -κρήνη) and "ancient" (archaios -αρχαίος). The reference is to the occurrence of many members of this kingdom in geothermal springs. It was first defined as a kingdom by Woese et al. (1990).

Hyperthermophilic archaea (Figures A&B) occur in areas that are rich in sulfur and very hot (Figure C). Such environments are associated with geothermal sites (geothermally heated soils and surface hot springs). They are the producers that form the foundation of the productive deep ocean geothermal vent environments, called sulfotara. This is a problematic group of Archaea (indeed, almost all Archaea are problematic). They metabolize sulfur and generally grow at temperatures approaching the boiling point of water, both of which likely are primitive characters.

*A. A TEM micrograph of Thermoproteus.*	*B. A TEM micrograph of Sulfolobus.*	*C. A hot sulfur spring in Yellowstone National Park, an environment in which Sulfolobus* thrives.**
Images taken from: A: http://hanskrause.de/HKHPE/hkhpe_02_06.htm B: http://web.pdx.edu/~kstedman/research.html C: http://www.nps.gov/yell/slidefile/thermalfeatures/hsandterraces/mudvolcano/page.htm

SYNOPTIC DESCRIPTION OF THE CRENARCHAEOTA

The following description of the phylum Crenarchaeota comes from Brock et al. (1994), Margulis and Schwartz (1998), Garrity et al. (2001 and 2003), and Black (2002).

I. SYNONYMS: Extreme thermophiles, or sulfur-dependent archaebacteria.

II. PHYLUM CHARACTERISTICS:

A. Structure

Cell Form: Rods, discs, cocci, filaments.

Cell Wall: Not rigid; gram-.

Motility: Non-motile.

B. Physiology

O₂ TOLERANCE: Most are strict anaerobes; 2 are aerobic.

Substrates: Facultative chemoautotrophs (lithotrophs) using elemental sulfur as an energy source. Others are heterotrophic and oxidize organic compounds in the presence of oxygen or sulfur. Some can ferment organic compounds (to CO₂ and fatty acids).

Products: The lithotrophic organisms produce H₂SO₄, Fe₂(SO₄), and H₂S. The heterotrophic species produce CO₂, H₂S, and fatty acids.

C. Other: They are the most thermophilic of all known bacteria. They have cholesterol (and perhaps other sterols) associated with the membranes.

D. Ecology: They grow in hot, sulfur-rich environments, called Solfatara. Such environments include hot sulfur springs which are mildly to very acidic; 60-110C. They also include submarine volcanic vents.

SYSTEMATICS OF THE CRENARCHAEOTA

Although, the fundamental synapomorphies do not seem to have been defined for the Crenarchaeota, the group seems to be well supported by 16S rRNA sequence trees. Mindful of that, I have followed the system of Garrity et al. (2001 and 2003) for this phylum. Still, I recognize that the group as it is defined likely is paraphyletic.

HIERARCHICAL CLASSIFICATION OF THE CRENARCHAEOTA

I removed the thermoacidobacteria and other taxa like Archaeoglobus from this kingdom after Garrity et al. (2001 and 2003). In general, this system follows that of Garrity et al. (2001 and 2003) in which the phylum has a single class with three orders.

CLASS THERMOPROTEI

ORDER THERMOPROTEALES

Rods and filaments, less than a micrometer wide but up to 100 micrometers long. Often with irregular, swollen protuberances on the cell surfaces. Growth maxima at temperatures between 75 and 100C; and pH between 4.5 and 7.

Thermoproteus, Caldivirga, Pyrobaculum, Thermocladium, Thermofilum.

ORDER DESULFUROCOCCALES

Discoid or spherical (coccoid) cells (0.3 to 2.5 micrometers). Growth maxima at temperatures above 85C and pH between 4.5 and 7.

Desulfurococcus, Aeropyrum, Ignicoccus, Staphylothermus, Stetteria, Sulfobococcus, Thermodiscus, Thermosphaera, Hyperthermus, Pyrobolus.

ORDER SULFOLOBALES

Cells coccoid or lobed, 0.8 to 2 micrometers in diameter. Growth maxima at temperatures between 60 and 90C and pH between 2 and 4.5.

Sulfolobus, Acidianus, Metallosphaera, Stygiolobus, Sulfurisphaera, Sulfurococcus.

This page is maintained by Jack R. Holt. Last revised: 02/07/2008.