Aquificales
| Aquificae | |
|---|---|
| Scientific classification | |
| Domain: | Bacteria |
| Phylum: |
Aquificae Reysenbach 2002 emend. Gupta & Lali 2014 |
| Class: |
Aquificae Reysenbach 2002 emend. Gupta & Lali 2014 |
| Orders & Families | |
| Synonyms | |
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The Aquificae phylum is a diverse collection of bacteria that live in harsh environmental settings. The name 'Aquificae' was given to this phylum based on an early genus identified within this group, Aquifex (“water maker”), which is able to produce water by oxidizing hydrogen. They have been found in springs, pools, and oceans. They are autotrophs, and are the primary carbon fixers in their environments. These bacteria are Gram-negative, nonspore-forming rods. They are true bacteria (domain Bacteria) as opposed to the other inhabitants of extreme environments, the Archaea.
The Aquificae currently contain 15 genera and 42 validly published species. The phylum comprises a single class and two orders. Aquificales consists of the families Aquificaceae and Hydrogenothermaceae, while the Desulfurobacteriaceae are the only family within the Desulfobacteriales. Thermosulfidibacter takaii is not assigned to a family within the phylum based on its phylogenetic distinctness from both orders. It is currently classified as a member of Aquificales, but it has shown more physiological similarity to the Desulfobacteriaceae.
Comparative genomic studies have identified several conserved signature indels (CSIs) that are specific for all species belonging to the phylum Aquificae and provide potential molecular markers. The order Aquificales can be distinguished from Desulfobacteriales by several CSIs across different proteins that are specific for each group. Additional CSIs have been found at the family level, and can be used to demarcate Aquificae and Hydrogenothermaceae from all other bacteria. In parallel with the observed CSI distribution, the orders within the Aquificae are also physiologically distinct from one another. Members of the Desulfurobacteriales are strict anaerobes that exclusively oxidize hydrogen for energy, whereas those belonging to the Aquificales are microaerophilic, and capable of oxidizing other compounds (such as sulfur or thiosulfate) in addition to hydrogen.
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