Haloferax volcanii is a species of organism in the genus Haloferax in the Archaea.
Description and significance
Microbiologist Benjamin Elazari Volcani first discovered Haloferax volcanii, a self-named extremophile, in the 1930s. H. volcanii is a halophilic mesophile archaeon that can be isolated from hypersaline environments such as: the Dead Sea, the Great Salt Lake, and oceanic environments with high sodium chloride concentrates. Haloferax volcanii is noteworthy because it can be cultured without much difficulty, rare for an extremophile. H. volcanii is chemoorganotrophic, metabolizing sugars as a carbon source. It is primarily aerobic, but is capable of anaerobic respiration under anoxic conditions. Recently an isolate of this species was studied by researchers at University of California, Berkeley, as part of a project on the survival of haloarchaea on Mars.
Genome structure
The genome of H. volcanii consists of a large (4 Mb), multicopy chromosome and several megaplasmids. The complete genome of the wild-type strain of H. volcanii (DS2) consists of about 4130 genes.
The genome has been completely sequenced and a paper discussing it was published in 2010. The molecular biology of H. volcanii has been extensively studied for the last decade in order to discover more about DNA replication, DNA repair and RNA synthesis. The archaeal proteins used in these processes are extremely similar to Eukaryotic proteins and so are studied primarily as a model system for these organisms. H. volcanii undergoes prolific horizontal gene transfer through a mechanism of "mating"- cell fusion.
Cell structure and metabolism
Reproduction among H. volcanii occurs asexually by binary fission. This practice is similar to that of other Archaea and, indeed, that of bacteria.
Like many archaea, H. volcanii cells have no cell wall and therefore are dependent on other mechanisms, such as their S-layer and cytoskeletal proteins, for structure. An individual H. volcanii archaeon can vary from 1-3 micrometers in diameter. They are pleomorphic, generally transitioning from motile, elongated rod shapes to stationary, biofilm-generating disk shapes as the culture ages. Additionally, biofilms generated by H. volcanii are capable of rapidly producing honeycomb patterns when exposed to changes in humidity. The membranes of this organism are made of the typical ether linked membrane lipids found solely in archaea and also contain a high level of carotenoids including lycopene, which gives them their distinctive red color.
H. volcanii use a salt in method to maintain osmostasis, rather than the typical compatible solutes method seen in bacteria. This method involves the maintenance of a high degree of potassium ions in the cell to balance the sodium ions outside. For this reason, H. volcanii has a complex ion regulation system.
H. volcanii will optimally grow at 42 °C in 1.5-2.5 M NaCl and complex nutrient medium. It will still grow at 37 °C, but still requires the concentrated NaCl and complex medium.
Due to the salt in method cytoplasmic proteins are structured to fold in the presence of high ionic concentrations. As such, they typically have a large number of charged residues on the exterior section of the protein and very hydrophobic residues forming a core. This structure considerably increases their stability in saline and even high temperature environments but comes at some loss of processivity compared to bacterial homologs.
H. volcanii respire as their sole source of ATP, unlike several other halobateriacae, such as Halobacterium salinarum they are incapable of photophosphorylation as they lack the necessary bacteriorhodopsin.
Ecology
Isolates of H. volcanii are commonly found in high-salinity aquatic environments, such as the Dead Sea. Their precise role in the ecosystem is uncertain, but the carbohydrates contained within these organisms potentially serve many practical purposes. Because of their ability to maintain homeostasis in spite of the salt around them, H. volcanii could be an important player in advancements in biotechnology. As it is likely that H. volcanii and comparable species are ranked among the earliest living organisms, they also provide information related to genetics and evolution.