Halobacteriaceae is a
family in the order
Halobacteriales and the domain
Archaea.[1]Halobacteriaceae represent a large part of
halophilic Archaea, along with members in two other methanogenic families, Methanosarcinaceae and Methanocalculaceae.[2] The family consists of many diverse genera that can survive extreme environmental niches.[3] Most commonly, Halobacteriaceae are found in hypersaline lakes and can even tolerate sites polluted by heavy metals.[4] They include
neutrophiles,
acidophiles (ex. Halarchaeum acidiphilum),
alkaliphiles (ex. Natronobacterium), and there have even been
psychrotolerant species discovered (ex.
Hrr. lacusprofundi).[3] Some members have been known to live aerobically, as well as anaerobically, and they come in many different
morphologies.[3] These diverse morphologies include rods in genus
Halobacterium, cocci in
Halococcus, flattened discs or cups in
Haloferax, and other shapes ranging from flattened triangles in
Haloarcula to squares in
Haloquadratum, and
Natronorubrum.[5][6] Most species of Halobacteriaceae are best known for their high salt tolerance and red-pink pigmented members (due to bacterioruberin carotenoids[5]), but there are also non-pigmented species and those that require moderate salt conditions.[3][7] Some species of Halobacteriaceae have been shown to exhibit
phosphorus solubilizing activities that contribute to
phosphorus cycling in hypersaline environments.[8] Techniques such as
16S rRNA analysis and
DNA-DNA hybridization have been major contributors to taxonomic classification in Halobacteriaceae, partly due to the difficulty in culturing halophilic Archaea.[7][3][2]
Overview
Halobacteriaceae are found in water saturated or nearly saturated with salt. They are also called
halophiles, though this name is also used for other organisms which live in somewhat less concentrated salt water. They are common in most environments where large amounts of salt, moisture, and organic material are available. Large blooms appear reddish, from the pigment
bacteriorhodopsin. This pigment is used to absorb light, which provides energy to create
ATP. Halobacteria also possess a second pigment,
halorhodopsin, which pumps in chloride ions in response to photons, creating a voltage gradient and assisting in the production of energy from light. The process is unrelated to other forms of
photosynthesis involving electron transport and halobacteria are incapable of
fixing carbon from
carbon dioxide.
Halobacteria can exist in salty environments because although they are
aerobes, they have a separate and different way of creating energy through use of light energy. Parts of the
membranes of halobacteria are purplish in color and contain retinal
pigment. This allows them to create a
proton gradient across the membrane of the cell which can be used to create
ATP for their own use.
They have certain adaptations to live within their salty environments. For example, their cellular machinery is adapted to high salt concentrations by having charged amino acids on their surfaces, allowing the cell to keep its water molecules around these components. The osmotic pressure and these amino acids help to control the amount of salt within the cell. However, because of these adaptations, if the cell is placed in a wet, less salty environment, it is likely to immediately burst from the osmotic pressure.
Grant WD, Larsen H (1989). "Group III. Extremely halophilic archaeobacteria. Order Halobacteriales ord. nov.". In JT Staley, MP Bryant, N Pfennig, JG Holt (eds.). Bergey's Manual of Systematic Bacteriology, Volume 3 (1st ed.). Baltimore: The Williams & Wilkins Co. p. 169.
Gibbons, NE (1974). "Family V. Halobacteriaceae fam. nov.". In RE Buchanan and NE Gibbons (ed.). Bergey's Manual of Determinative Bacteriology (8th ed.). Baltimore: The Williams & Wilkins Co.