''Haloferacales'' is an order of

halophilic The halophiles, named after the Greek word for "salt-loving", are extremophiles that thrive in high salt concentrations. While most halophiles are classified into the domain Archaea, there are also bacterial halophiles and some eukaryotic species, ...

chemoorganotrophic Primary nutritional groups are groups of organisms, divided in relation to the nutrition mode according to the sources of energy and carbon, needed for living, growth and reproduction. The sources of energy can be light or chemical compounds; the ...

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

archaea within the class

Haloarchaea Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of t ...

. The type genus of this order is ''

Haloferax In taxonomy, ''Haloferax'' (common abbreviation: ''Hfx.'') is a genus of the Haloferacaceae. Genetic exchange Cells of ''H. mediterranei'' and cells of the related species '' H. volcanii'' can undergo a process of genetic exchange between two ...

.'' The name ''Haloferacales'' is derived from the Latin term ''Haloferax,'' referring to the type genus of the order and the suffix "-ales," an ending used to denote an order. Together, ''Haloferacales'' refers to an order whose nomenclatural type is the genus ''

.''

Biochemical Characteristics and Molecular Signatures

Members are halophiles and can be chemoorganotrophs or heterotrophs and are isolated from high-salt environments such as marine solar salterns and the

Dead Sea The Dead Sea ( he, יַם הַמֶּלַח, ''Yam hamMelaḥ''; ar, اَلْبَحْرُ الْمَيْتُ, ''Āl-Baḥrū l-Maytū''), also known by other names, is a salt lake bordered by Jordan to the east and Israel and the West Bank ...

. Some members are motile and contain gas vesicles. Morphology is variable, including rod, coccus or flat square shapes. Members of this order grow optimally in neutral pH. The DNA G+C content for this order ranges between 55-66 mol%. This order can be reliably distinguished from other Halobacteria by the presence of five conserved signature proteins (CSPs) and four

conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

(CSIs) present in the following proteins:

DNA gyrase DNA gyrase, or simply gyrase, is an enzyme within the class of topoisomerase and is a subclass of Type II topoisomerases that reduces topological strain in an ATP dependent manner while double-stranded DNA is being unwound by elongating RNA-poly ...

B, prolyl t-RNA synthetase, acyl-CoA synthetase and aspartyl/glutamyl-tRNA amido-transferase subunit B.

Historical Systematics and Current Taxonomy

As of 2021, ''Haloferacales'' contains two families, ''

Haloferacaceae ''Haloferacaceae'' is a family of halophilic, chemoorganotrophic or heterotrophic archaea within the order '' Haloferacales.'' The type genus of this family is ''Haloferax.'' Its biochemical characteristics are the same as the order '' Haloferaca ...

'' and ''

Halorubraceae ''Halorubraceae'' is a family of halophilic, chemoorganotrophic or heterotrophic archaea within the order ''Haloferacales.'' The type genus of this family is ''Halorubrum''. Its biochemical characteristics are the same as the order ''Haloferacales ...

''. Members of this order was demarcated from the class

Halobacteria Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of the Euryarchaeota, found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of th ...

, previously a large phylogenetically unrelated group of species with distinct biochemical characteristics and different ecological niches. The diverse range of morphological and physiological characteristics made it difficult to clarify the evolutionary relationship within the class beyond a genus level. In 2015, Gupta et al. proposed the division of the class

into the orders ''

Halobacteriales In taxonomy, the Halobacteriales are an order of the Halobacteria, 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 ...

, Haloferacales and

Natrialbales ''Natrialbales'' is an order of halophilic, chemoorganotrophic archaea within the class Haloarchaea. The type genus of this order is ''Natrialba.'' The name ''Natrialbales'' is derived from the Latin term ''Natriabla,'' referring to the type gen ...

'' based on comparative genomic analyses and the branching pattern of various phylogenetic trees constructed from several different datasets of conserved proteins and 16S rRNA sequences. Molecular markers, specifically

, specific to this order were also identified as evidence supporting the division independent of phylogenetic trees. Each order can be reliably distinguished from each other and other species based on the presence of these CSIs.

References

{{Archaea classification Halobacteria

Biochemical Characteristics and Molecular Signatures

Historical Systematics and Current Taxonomy

See also

References