Cells of H. mediterranei and cells of the related species H. volcanii can undergo a process of genetic exchange between two cells which involves cell fusion resulting in a heterodiploid cell (containing two different chromosomes in one cell).[3] Although this genetic exchange ordinarily occurs between two cells of the same species, it can also occur at a lower frequency between an H. mediterranei and an H. volcani cell. These two species have an average nucleotide sequence identity of 86.6%.[3] During this exchange process, a diploid cell is formed that contains the full genetic repertoire of both parental cells, and genetic recombination is facilitated. Subsequently, the cells separate, giving rise to recombinant cells.
Taxonomy
As of 2022, 13 species are validly published under the genus Haloferax.[1]
Proposed species
Several species and novel binomial names have been proposed, but not validly published.
"Haloferax antrum" Enache et al. 2006,[4] "Haloferax opilio" Enache et al. 2006, "Haloferax rutilus" Enache et al. 2006 and "Haloferax viridis" Enache et al. 2006 were isolated from Romanian salt lakes and first proposed as new species in 2006.[5] Only H. prahovense, that was proposed along them has since been validly published.
"Haloferax berberensis" Kharroub et al. 2005e was isolated in Algeria and proposed as new species in 2005.[6]
Haloferax litoreum, Haloferax marinisediminis and Haloferax marinum were first published in 2021, but are not accepted as of 2022.[7]
Haloferax marisrubri and Haloferax profundi were first published in 2020, but is not accepted as of 2022.[8]
Haloferax massilisiensis or Haloferax massiliense was first published in 2016 and again in 2018 as human associated halophilic archaeon. As of 2022, this species is not accepted.[9]
Several Haloferax species, especially Haloferax mediterranei have gained eminence for their ability to serve as an efficient chassis for bioproduction. H. mediterranei is a well-known producer of polyhydroxyalkanoates, a sustainable and biodegradable bioplastic.[16] They have been studied for the production of several value-added products such as bioplastics, pigments and exoenzymes.[17]H. mediterranei is capable of accumulating high amounts of both homopolymer PHAs and co-polymer PHAs from a wide array of sustainable carbon substrates.[16][18]Haloferax species have also been used to produce industrially relevant exoenzymes such as laccase for bioprocessing.[19] Since they can thrive in extreme conditions of salinity, toxicity, heavy metal exposure and UV radiation, the fermentation costs are significantly lowered as the chance of contamination is reduced.[17] In hypersaline environments like the Dead Sea & Great Salt Lake, Haloferax species shoulder most of the responsibility of denitrification.[20] These strains could be leveraged for nitrogen removal systems designed to remediate saline effluents from fisheries, textile industries and food processing plants.
Torreblanca M, Rodriquez-Valera F, Juez G, Ventosa A, Kamekura M, Kates M (1986). "Classification of non-alkaliphilic halobacteria based on numerical taxonomy and polar lipid composition, and description of Haloarcula gen. nov. and Haloferax gen.nov". Syst. Appl. Microbiol. 8 (1–2): 89–99. doi:10.1016/s0723-2020(86)80155-2.
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