Chthonomonas calidirosea  Chthonomonas calidirosea is a Gram-negative bacterium and also the first representative of the new class Chthonomonadetes within the phylum Armatimonadetes. The Armatimonadetes were previously known as candidate phylum OP10. OP10 was composed solely of environmental 16S rRNA gene clone sequences prior to "C. calidirosea's" relative, "Armatimonas rosea's" discovery. It is now known that bacterial communities from geothermal environments, are generally constituted by, at least 5–10% of bacteria belonging to Armatimonadetes. "Chthonomonas calidirosea" was originally isolated from geothermally heated soil at Hell's Gate, Tikitere, New Zealand. The soil was aseptically sampled at an approximate depth of 15 cm below the surface. The sampled soil had a pH of 4.3 and an "in situ" temperature of 55 °C. The environmental 16S rRNA gene sequences, belonging to the phylum "Armatimonadetes" are currently sorted into six groups. Groups 2, 5, and 6 consist solely of sequences. Group 1 contains "Armatimonadetes rosea", Group 3 contains "Chthonomonadetes calidirosea", and Group 4 contains "Fimbriimonas ginsengisoli". "Armatimonas rosea", an aerobic, Gram-negative, pink pigmented, nonmotile, ovoid/rod shaped bacterium, was isolated from the rhizoplane of an aquatic plant "Phragmites australis" in Japan. It is the first representative of the phylum Armatimonadetes. "Fimbriimonas ginsengisoli", an aerobic, non-motile, mesophilic, rod-shaped bacterium, was isolated from a ginseng field soil sample. It represents the first cultured representative of the Fimbriimonadia class, corresponding with Group 4 of the phylum Armatimonadetes. When grown on solid medium AOM1, colonies were light-pink pigmented, circular, convex, relatively small (2–4 mm) in size after one week of incubation at 60 °C. "Chthonomonas calidirosea" has an optimum temperature at 68 °C with a range of 50–73 °C.