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Aquificae bacteria

Black-smoker chimney field at 345-m water depth, East Diamante volcano, United States, Mariana Islands.
Source: Sound Waves

The phylum Aquificae is considered to be one of the earliest branching groups within the Bacteria. The members of this group are rod-shaped, moderately thermophilic to hyperthemophilic. Most members of Aquificae are motile, growing bets between pH 6.0 and 8.0. The only exception is Hydrogenbacter acidophilis, which grows at pH 3-4. This phylum consists of a single class Aquificae and order Aquificales. Some representative genera are Aquifex, Calderobacterium, Hydrogenbacter, and Thermovrinis. Aquificae bacteria have been isolated from hot springs, volcano calderas, and marine hydrothermal vents. These bacteria thrive at 86-95°C, making them some of the most thermophilic bacteria known. Members of this group appear to be restricted to geothermal habitats, where they live by splitting hydrogen gas of hydrogen sulfide and fixing carbon dioxide for carbon. The Aquificae include halophiles, isolated from saline hot springs, and acidophiles, isolated from an acidic sulfur deposit.

The majority of the Earth's habitable environments are physically located in environments that do not receive sunlight. Indeed, the largest potential habitats on Earth are located in the ocean, which covers approximately 70% of the Earth's surface. These dark ocean environments (Fig. 2 to ​to5)5) together comprise the largest collection of habitats by volume that life—in particular, microbial life—can occupy on Earth. Hydrothermal chimneys (active, hot, venting sulfide structures) are a globally dispersed habitat on the seafloor. Members of the phylum Aquificae have been observed only in active hydrothermal sulfide chimneys and are absent from inactive sulfides.3


  1. Assembling the tree of life. Joel Cracraft, Michael J. Donoghue
  2. Principles of Microbiology. McGraw-Hill Education, 2009
  3. Microbial Ecology of the Dark Ocean above, at, and below the Seafloor


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