Register list for 16 new names including Fervidibacteria classis nov.

Members of the order are aerobic or anaerobic, with both high- and low-affinity terminal oxidases present in the aerobic Fervidibacterales. All members are likely polysaccharide degraders as numerous carbohydrate active enzymes are found in all members of the order. Phylogenomics and relative evolutionary divergence places this order in the class Fervidibacteria.

Genomes belonging to the genus have been recovered from metagenomic sequence data from thermal environments in Antarctica, Canada, China, Japan, and USA. GC content within the genus range between 49% to 59%. Phylogenomic congruence and relative evolutionary divergence along with ANI and AAI values support designation of this group as a genus. ANI values among species in the genus are below species delineation guidelines. Available genome data support members of the genus largely being aerobic or microaerophilic, with subunits of both the high-affinity and low-affinity terminal oxidases encoded within the genus. Numerous glycoside hydrolases are encoded by species in the genus, supporting a likely saccharolytic lifestyle for members of the genus.

Genomes belonging to the genus have been recovered from metagenomic sequence data from thermal environments in the USA and China. GC content range between 47% and 53%. ANI and AAI values among species are inconsistent, although all ANI values between species are below suggested species guidelines. Based on available genome data, the genus is strictly anaerobic. Between 64 and 105 glycoside hydrolases (GHs) are encoded by genomes of the genus, with > 25 GH families represented. Group 1a and 4b hydrogenases are conserved within the genus, suggesting hydrogen and formate metabolism in the genus. The core of the methyl-branch of the Wood-Ljungdahl pathway is conserved in the genus.

Hyperthermophilic, microaerophilic, facultatively anaerobic, and grows chemoheterotrophically on monosaccharides and polysaccharides. Cells are ovoid- to rod-shaped, Gram-stain negative, and are 0.9-1.3 µm in width and 1.6-3.6 µm in length. Grows between 65 and 87.5 °C and an optimum temperature of 80 °C, and a pH range of 6.5-8.6 with an optimum pH of 7.5. Grows at an optimum O2 concentration of 5-10%. Grows on D-arabinose, D-galactose, D-glucose, D-rhamnose, D-ribose, D-xylose, chondroitin sulfate, colloidal chitin, galactan, gellan gum, guar gum, karaya gum, locust bean gum, xantham gum, xyloglucan, β-glucan, glycogen, starch, AFEX-pretreated corn stover, miscanthus, sugarcane bagasse, acetate and casamino acids. Grows weakly on xyloglucan under fermentation conditions. The major fatty acids (> 10%) are C16:0, C18:0 and/or cyclo-C17:0, and iso-C16:0. The major respiratory quinones (> 10%) are MK-8 and MK-9. The isolate and genomes of the species have been recovered from geothermal springs in the Great Basin, Nevada, USA. GC content of genomes range between 51-52%. Subunits for both the high-affinity and low-affinity terminal oxidases are encoded in the genomes. Genomes also encode a Group 3d [NiFe] hydrogenase, which produces hydrogen as an electron sink for NAD+ regeneration.

The sole genome representative of this species was recovered from a metagenome from Hishikari Mine, Japan. The GC content if 59%. The genome encodes both the high- and low-affinity terminal oxidases.