Thermomicrobia

In 1973, a strain of rose-pink thermophilic bacteria was isolated from Toadstool Spring in Yellowstone National Park, which was later named Thermomicrobium roseum and proposed as a novel species of the novel genus Thermomicrobium. At that time the genus was categorized under family Achromobacteraceae, but it became a distinct phylum by 2001. In the same year, another strain of rose-pink thermophilic bacteria was isolated from Yellowstone National Park, which was named Thermobaculum terrenum. Later analysis based on genome put this species under Thermomicrobia class. However, the current standing of Thermobaculum terrenum is disputed. While it has nitrite-oxidizing activity, which is unique in the Thermomicrobia class, it is placed under the Thermomicrobia class based on 16s rRNA phylogeny. In 2014, two thermophilic, Gram-positive, rod-shaped, non-spore-forming bacteria (strains KI3T and KI4T) isolated from geothermally heated biofilms growing on a tumulus in the Kilauea Iki pit crater on the flank of Kilauea Volcano (Hawaiʻi) were proposed as representatives of new species based on 16s rRNA phylogeny. The KI3T strain, later named as Thermomicrobium carboxidum, is closely related to Thermomicrobium roseum. The KI4T strain, later named as Thermorudis peleae, was proposed as a type strain of new genus Thermorudis. In 2015, a thermophilic bacteria strain WKT50.2 isolated from geothermal soil in Waitike (New Zealand) was proposed to be a novel species, later named Thermorudis pharmacophila. Phylogenic analysis based on 16s rRNA place it within Thermomicrobia class, as close relative to Thermorudis peleae. == Characteristics ==

Living environment Members of the class Thermomicrobia are broadly distributed across a wide range of both aquatic and terrestrial habitats. Thermomicrobium roseum was found in geothermally heated hot springs, Thermorudis pharmacophila and Thermobaculum terrenum from heated soils, and Thermomicrobium carboxidum and Thermorudis peleae from heated sediments In addition, Sphaerobacter thermophilus was found in sewage sludge that went through thermophilic treatment. However, species of this class do share some features, as listed below: • All members except Thermobaculum terrenum have inability to utilize some common monosaccharides (e.g. glucose, fructose, etc.) as sole carbon source. Thermomicrobium carboxidum and Thermorudis peleae show resistance against both of those antibiotics, while Sphaerobacter thermophilus shows resistance against only metronidazole. The same feature was found in Sphaerobacter thermophilus and Thermorudis pharmacophila. Meanwhile, other members of Thermomicrobia class are reported to be Gram-positive and have typical monoderm cell envelope. There are some possible explanations of the inconsistency of Gram-staining result within the class. For Thermorudis pharmacophila, a possible explanation suggested by Houghton et al. is that it is actually an atypical monoderm bacterium, because its cell envelope contains amino acids usually associated with Gram-positive bacteria, have reaction to KOH, vancomycin and ampicillin, and lacks genes responsible for diderm formation. It is also suggested that further study is required to resolve this problem, since the inconsistent reports of cell envelope structure are found for the whole Chloroflexota phylum. ==Phylogeny==

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). • Order Sphaerobacterales Stackebrandt, Rainey & Ward-Rainey 1997 • Family Sphaerobacteraceae Stackebrandt, Rainey & Ward-Rainey 1997 • Genus Sphaerobacter Demharter et al. 1989 • S. thermophilus Demharter et al. 1989 • Genus Nitrolancea Sorokin et al. 2014 • N. hollandica Sorokin et al. 2014 • "Ca. N. copahuensis" Spieck et al. 2020 • Order Thermomicrobiales Garrity & Holt 2002 • Family Thermomicrobiaceae Garrity & Holt 2002 • Genus Thermalbibacter Zhao et al. 2023 • T. longus Zhao et al. 2023 • Genus Thermomicrobium Jackson, Ramaley & Meinschein 1973 • T. carboxidum King & King 2014 • T. roseum Jackson, Ramaley & Meinschein 1973 • Genus Thermorudis King & King 2014 • T. peleae King & King 2014 • T. pharmacophila Houghton et al. 2015 ==See also==