Kos.mo.to'ga. Gr. masc. n. kosmos universe or world; L. fem. n. toga , a Roman outer garment; N.L. fem. n. Kosmotoga a worldly toga, referring to the diverse environments inhabited by members of this Thermotogota genus (oil reservoirs, marine hydrothermal sediments, hydrothermal vents, and crustal fluids). Thermotogota / Thermotogae / Kosmotogales / Kosmotogaceae / Kosmotoga The genus Kosmotoga comprises anaerobic thermophilic heterotrophs , with optimum growth temperatures of 60–70°C, optimal pH of 7.0, and optimal salinities between 1.5 and 3.0 (NaCl w/v%). These bacteria reduce sulfur, thiosulfate, or cystine to H 2 S . The cells are Gram‐negative, and diverse morphologies are observed, from short rods to cocci. Kosmotoga spp. are members of the phylum Thermotogota , class Thermotogae , order Kosmotogales , and family Kosmotogaceae . The genus currently consists of four described species: Kosmotoga arenicorallina , Kosmotoga olearia , Kosmotoga pacifica , and Kosmotoga shengliensis . Known habitats are oil reservoirs, hydrothermal vents, marine sediments, and crustal fluids. DNA G + C content (mol%) : 36.4–42.5. Type species : Kosmotoga olearia DiPippo et al. 2009 VP .

Ther.mo.to.ga.ce'ae. N.L. fem. n. Thermotoga , type genus of the family; L. suff. ‐ aceae , ending to denote a family; N.L. fem. pl. n. Thermotogaceae , the family of Thermotoga . Thermotogota / Thermotogae / Thermotogales / Thermotogaceae The family Thermotogaceae comprises sheathed thermophilic and hyperthermophilic, anaerobic, fermentative, and hydrogen‐producing bacteria. Cells are rod shaped, occurring singly, in pairs, or in chains. Cells are surrounded with sheaths, the so‐called togas. In stationary phase, they might look like “balloons.” Gram‐negative. Colonies are circular, convex, and vary in color from white to cream. The members of the family grow well on complex organic media and utilize a broad spectrum of carbon sources. Optimal growth at 60–80°C. Reduce thiosulfate and, in some cases, elemental sulfur, to sulfide. The family currently accommodates two genera, Thermotoga and Pseudothermotoga . The members of the family were isolated from geothermal heated marine sediments, shallow submarine thermal vents, hot springs, solfataric springs, oil reservoirs, and thermophilic bioreactors. DNA G + C content (mol%) : 38.7–51.3%. Type genus : Thermotoga Stetter and Huber 1986, 575 VP (Effective publication: Stetter and Huber in Huber, Langworthy, Konig, Thomm, Woese, Sleytr et al., 1986, 332) emend. Bhandari and Gupta 2014, 163.

Me.so.a.ci.di.to.ga.ce'ae. N.L. fem. n. Mesoaciditoga type genus of the family; L. fen, pl. n. suff. ‐aceae, ending denoting a family; N.L. fem. pl. n. Mesoaciditogaceae , the Mesoaciditoga family. Thermotogota / Thermotogae / Mesoaciditogales / Mesoaciditogaceae The family Mesoaciditogaceae , the only family in the order Mesoaciditogales , comprises thermophilic, weakly acidophilic bacteria. The cells stain Gram‐negative and are sheathed short rods . Members of this family are heterotrophs and anaerobes , growing optimally at salinities that range from freshwater to marine seawater. Known habitats are deep‐sea hydrothermal vents and acidic terrestrial hot springs. The family currently accommodates two genera, Mesoaciditoga and Athalassotoga . Only two species have been described, but additional 16S rRNA sequences and metagenomes from environmental samples suggest that Mesoaciditogaceae may include additional genera whose representatives are not yet isolated. DNA G + C content (mol%) : 39.9–40.6 (genome analysis). Type genus : Mesoaciditoga Reysenbach et al. 2013 VP .

Kos.mo.to.ga.ce'ae. N.L. fem. n. Kosmotoga , type genus of the family; L. fem. pl. suff. ‐aceae , ending to denote a family; N.L. fem. pl. n. Kosmotogaceae , the family whose nomenclatural type is the genus. Thermotogota / Thermotogae / Kosmotogales / Kosmotogaceae The family Kosmotogaceae comprises mesophilic and thermophilic bacteria. The cells are Gram‐negative and sheathed short rods to ovoid cocci . Heterotrophs. Produce hydrogen or hydrogen sulfide . Optimal growth temperature between 37 and 70°C. Members of the family reduce thiosulfate and/or sulfur to sulfide. The family currently accommodates two genera, Kosmotoga and Mesotoga . Known habitats are hydrothermal vents, marine sediments, crustal fluids, deep aquifers, oil reservoirs, hydrocarbon‐impacted environment, and anaerobic man‐made environments. DNA G + C content (mol%) : 36.4–48.3. Type genus : Kosmotoga Dipippo et al. 2009 VP emend. Nunoura et al. 2010.

Pseu.do.ther.mo.to'ga. Gr. adj. pseudo , false; N.L. fem. n. Thermotoga, a bacterial genus; N.L. fem. n. Pseudothermotoga, a genus falsely (or incorrectly) classified as Thermotoga . Thermotogota / Thermotogae / Thermotogales / Thermotogaceae / Pseudothermotoga The genus Pseudothermotoga comprises sheathed, thermophilic, anaerobic, fermentative, and hydrogen‐producing bacteria. Thiosulfate is reduced by all the strains of the genus. Pseudothermotoga spp. are members of the phylum Thermotogota , class Thermotogae, order Thermotogales , family Thermotogaceae . Known habitats are hot springs, oil reservoirs, and thermophilic bioreactors. Genome sizes are in the range 2.01–2.19 Mb, and GC content varies between 38.7 and 51.3%. Based on phylogenomic analyses, two recently described species, Thermotoga profunda and Thermotoga caldifontis, should be assigned to the recently described genus Pseudothermotoga . Based on DNA–DNA hybridization and various genomic measurements, the Pseudothermotoga lettingae and Pseudothermotoga subterranea species should be reclassified as subspecies of Pseudothermotoga elfii . With these proposed reclassifications, the genus Pseudothermotoga would consist of five described species: Pseudothermotoga thermarum, Pseudothermotoga elfii, Pseudothermotoga hypogea, Pseudothermotoga Profunda, and Pseudothermotoga caldifontis . However, high genomic divergence observed within this genus may require additional taxonomic revisions in the future. DNA G + C content (mol%) : 38.7–51.3. Type species : Pseudothermotoga thermarum Bhandari and Gupta, 2014, VL158 (Basonym: Thermotoga thermarum, Windberger et al. 1989 ).

Me'so.a.ci.di.to'ga Gr. masc. adj. mesos , middle; L. neut. adj. acidum , an acid, tart; from L. adj. acidus ‐a ‐um , sour; L. fem. n. toga , Roman outer garment, toga; N.L. fem. n. Mesoaciditoga , a moderately acidophilic toga. Thermotogota / Thermotogae / Mesoaciditogales / Mesoaciditogaceae / Mesoaciditoga The genus Mesoaciditoga is currently composed of one described species, Mesoaciditoga lauensis . It is a member of the phylum Thermotogota , class Thermotogae , order Mesoaciditogales , family Mesoaciditogaceae . M. lauensis is thermophilic, slightly acidophilic, and grows at seawater salinities. These bacteria ferment sugars and proteinaceous compounds and reduce sulfur to hydrogen sulfide. The cells are short rods with a sheath‐like structure and stain Gram‐negative. Known habitats are deep‐sea hydrothermal vents. DNA G + C content (mol%) : 39.9 (genome sequence). Type species : Mesoaciditoga lauensis Reysenbach et al. 2013 VP .

A.tha.las.so.to'ga Gr. pref. a ‐, not; Gr. fem. n. thalassa , sea; L. fem. n. toga , Roman outer garment, toga; N.L. fem. n. Athalassotoga , a non‐sea, or terrestrial, occurring toga. Thermotogota / Thermotogae / Mesoaciditogales / Mesoaciditogaceae / Athalassotoga The genus Athalassotoga is currently composed of one described species, Athalassotoga saccharophila . It is a member of the phylum Thermotogota , class Thermotogae , order Mesoaciditogales , family Mesoaciditogaceae . It is a thermophile , weakly acidophile, and grows at salinities between 0% and 0.75% NaCl (optimum 0%). It grows anaerobically and heterotrophically by fermentation of sugars and proteinaceous compounds. Its growth is stimulated by thiosulfate, l ‐cystine, and iron (III). The cells are short rods with a sheath‐like structure. Known habitats are acidic terrestrial hot springs. DNA G + C content (mol%) : 40.6 (genome sequence). Type species : Athalassotoga saccharophila Itoh et al. 2016 VP .

Ther.mo.si'pho. Gr. fem. n. thermê , heat; L. masc. n. sipho , little pipe to suck drinks through, a tube; N.L. masc. n. Thermosipho , the hot tube, due to the sheath surrounding the bacteria. Thermotogota / Thermotogae / Thermotogales / Fervidobacteriaceae / Thermosipho The genus Thermosipho is currently composed of eight species ( Thermosipho africanus , Thermosipho melanesiensis , Thermosipho japonicus , Thermosipho geolei , Thermosipho atlanticus , Thermosipho affectus , Thermosipho globiformans , and Thermosipho activus ). The rods are surrounded by an outer sheath‐like toga, and some rods form spheroids during growth. The spheroids may produce “immature progenies” that are too small to contain a complete genome, which need further investigation to elucidate their function. The cells are obligately anaerobic , thermophilic , with optimum growth temperature of 65–75°C, optimal pH 6.0–7.5, and optimal growth under low salinity 2.0–3.0% NaCl. Heterotrophic growth . Sulfur is reduced to H 2 S by all the species, while thiosulfate is reduced by Thermosipho africanus and Thermosipho japonicus . Molecular hydrogen inhibits growth. Two described Thermosipho spp. are capable of de novo biosynthesis of vitamin B12. Members of the phylum Thermotogota , class Thermotogae , order Thermotogales , and family Fervidobacteriaceae . Known habitats are shallow and deep‐sea hydrothermal vents and deep subsurface oil reservoirs. DNA G + C content (mol%) : 29.5–31.5 ( T m and genome analysis). Type species : Thermosipho africanus Huber et al. 1989, VL31 emend. Ravot et al. 1996.