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THE EUBACTERIA
HOME SYLLABUS WEEKLY ASSIGNMENTS J. SYSTEMATIC BIOLOGY TAXA OF LIFE
KINGDOM THERMOTOGAE

INTRODUCTION TO THE THERMOTOGAE AND ITS SINGLE PHYLUM, THERMOBACTERIA

Thermotogae (ther-mo-TO-ge) is derived from a Greek root meaning hot (thermos -θερμός) and a Latin root for the garment of a Roman citizen (toga).  The name is derived from Thermotoga, a common genus in the group.  It also is descriptive of the kingdom in that many taxa inhabit hot springs and deep ocean vents, and have a specialized  outer covering called a toga.

A recently discovered group, the Thermobactera is unique according to its 16S rRNA sequences as well as its ecology.  The bacteria occur in deep ocean vents and other hot springs areas, some with temperatures approaching the boiling point.  They are characterized by the occurrence of an outer covering called a toga that is several times thicker than the cell wall.   

aquifex-pt1-kenyon.jpg (11404 bytes)

A. TEM micrograph of Aquifex with obvious polar flagella.

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B. TEM micrograph of Thermotoga with its outer covering or toga.
Images taken from:
A: http://biology.kenyon.edu/Microbial_Biorealm/bacteria/aquifex/aquifex.htm
B: http://www.jcsg.org/images/targets/thermotoga.jpg

SYNOPTIC DESCRIPTION OF THE THERMOBACTERIA

The following description comes mainly from Margulis and Schwartz (1998), Barnes (1984), Brock et al. (1994), and Tudge (2000). 

I. SYNONYMS: Thermophilic fermenters

II. PHYLUM CHARACTERISTICS:

A. Structure

Cell Form: Unicellular rods.

Cell Wall: Gram-.

Motility: With polar flagella.

B. Physiology

O2 Tolerance: Strict anaerobes.

Substrates: Fermenters of sugars, proteins, and other organic compounds. Aquifex oxidizes H2, S0, or thiosulfate with O2 (microaerophilic) or NO3-.

Products:

C. Other: Some are covered with a "toga".

D. Ecology: Very heat-resistant.  In deep ocean vents and hot springs.  Some occur at temperatures in excess of 90C.

SYSTEMATICS OF THE THERMOBACTERIA

I follow the system proposed by Margulis and Schwartz (1998) in which the taxa occupy a separate phylum (Thermotogae; B-14).  Bergey's Manual of Systematic Bacteriology, 2nd edition (Garrity et al. 2001) treats the taxa that I include in the Thermotogae as two phyla (BI and BII).  

HIERARCHICAL CLASSIFICATION OF THE THERMOBACTERIA

This system follows Margulis and Schwartz (1998) in that the taxa are united within one phylum.  However, the framework of the system comes from Garrity et al. (2001 and 2003).

CLASS AQUIFEXI

ORDER AQUAFICALES

Aquifex, Caulderobacterium, Hydrogenobacter, Thermocrinis, Desulfurobacterium (?).

CLASS THERMOTOGIAE

ORDER THERMOTOGALES

Thermotoga, Fervidobacterium, Geotoga, Petrotoga, Thermosipho

This page is maintained by Jack R. Holt. Last revised: 04/22/2008.