Metallosphaera hakonensis

Metallosphaera hakonensis was isolated in 1996 by Takayanagi et al. from a hot spring in the Hakone National Park in Kanagawa, Japan.^[1] Originally classified as a member of the genus Sulfolobus,^[1] Kurosawa et al. determined through genetic testing that the organism belongs to the Metallosphaera genus in 2003.^[2] Takayanagi et al. determined a 92% similarity with Sulfolobus species; however, Kurosawa et al. determined a 98% similarity with Metallosphaera species.^[1][2] Using the more accurate high-performance liquid chromatography method, Kurosawa et al. also determined a new G+C content (43.29%) that is characteristic of Metallosphaera species.^[2]

Takayanagi et al. collected a water sample from a hot spring in the Hakone National Park in Kanagawa, Japan, with a pH 1.5 and a temperature of 91.5 °C.^[1] A 1:10 mL dilution of the sample and modified Allen's medium, a media known to sustain Sulfolobus species, was made and incubated at 70 °C for about one week.^[1] This sample was then used to form a 1:9 mL dilution with Allen's media, and a portion streaked onto 1.0% Geltrite plates containing Allen's media during exponential growth.^[1] After incubation at 70 °C, an isolated colony of M. hakonensis was used to inoculate fresh broth, incubated, and plated.^[1] This procedure was performed an additional time to isolate the archaea.^[1]

M. hakonensis can grow in temperatures between 50 °C and 80 °C and between pH values 1.0 and 4.0.^[1] M. hakonensis's optimal growth conditions are 70 °C and pH 3.0.^[1] Some Metallosphaera species, such as M. prunae, are mobile by means of flagellum; however, M. hakonensis does not have a flagellum.^[2] M. hakonensis is gram-negative and has either spherical or irregular polyhedron-shaped cells (lobe-shaped cells), that are 0.9 to 1.1 ${\displaystyle \mu }$m in diameter.^[1]

M. hakonensis has genome that is about 2.3 Mbp long and has a G+C content of 43.29% determined through Ion Torrent Sequencing and assembled using the Newbler v. 2.8 software.^[3][4] M. hakonensis's genome contains 3,357 protein coding genes and 57 RNA genes determined using the Joint Genome Institute's gene calling methods and IMG's annotation pipeline^[3] Near neighbors include Metallosphaera prunae, M. sedula, and M. yellowstonensis.^[2] M. hakonensis has a 98% similarity in the 16S rRNA sequence to the other members of the genus Metallosphaera.^[2]

Genome sequencing of M. hakonensis has revealed the presence of genes coding for enzyme Urease, with genes present for subunits A and B.^[3] Urease catalyzes the degradation of urea to ammonia and bicarbonate.^[5] Sequences also revealed the presence of genes for haloacetate dehalogenase.^[3] Haloacetate dehalogenase catalyzes the conversion of haloacetate to glycolate and the halide ion(e.g. fluoride).^[3] M. hakonensis also contains the gene for maleylacetate reductase, a key component in biological degradation of halogenated aromatic organic compounds.^[6][3]

Organisms belonging to the genus Metallosphaera are found in extreme environments such as volcanic fields^[7] and hot waste material in mines.^[8]

M. hakonensis is an obligate aerobic chemolithoautotroph that utilizes sulfur oxidation as its main source of energy.^[1] M. hakonensis is capable of utilizing yeast extract (excluding sugars), L-glutamic acid, L-tryptophan, maltose, and sulfur compounds such as elemental sulfur and hydrogen sulfide as energy sources, similar to other Metallosphaera species.^[1][2] M. hakonensis exhibits poor growth in media containing L-glutamic acid, L-tryptophan, and maltose.^[1] One unique feature of M. hakonensis is its ability to utilize FeS clusters and the sulfur anion, tetrathionate (O₆S₄^2-).^[2]