A spirochaete or spirochete is a member of the phylum Spirochaetota, which contains distinctive diderm (double-membrane) gram-negative bacteria, most of which have long, helically coiled cells. Spirochaetes are chemoheterotrophic in nature, with lengths between 3 and 500 μm and diameters around 0.09 to at least 3 μm.
The Actinomycetota are a diverse phylum of Gram-positive bacteria with high G+C content. They can be terrestrial or aquatic. They are of great economic importance to humans because agriculture and forests depend on their contributions to soil systems. In soil they help to decompose the organic matter of dead organisms so the molecules can be taken up anew by plants. While this role is also played by fungi, Actinomycetota are much smaller and likely do not occupy the same ecological niche. In this role the colonies often grow extensive mycelia, like a fungus would, and the name of an important order of the phylum, Actinomycetales, reflects that they were long believed to be fungi. Some soil actinomycetota live symbiotically with the plants whose roots pervade the soil, fixing nitrogen for the plants in exchange for access to some of the plant's saccharides. Other species, such as many members of the genus Mycobacterium, are important pathogens.
Deinococcota is a phylum of bacteria with a single class, Deinococci, that are highly resistant to environmental hazards, also known as extremophiles. These bacteria have thick cell walls that give them gram-positive stains, but they include a second membrane and so are closer in structure to those of gram-negative bacteria.
Verrucomicrobiota is a phylum of Gram-negative bacteria that contains only a few described species. The species identified have been isolated from fresh water, marine and soil environments and human faeces. A number of as-yet uncultivated species have been identified in association with eukaryotic hosts including extrusive explosive ectosymbionts of protists and endosymbionts of nematodes from genus Xiphinema, residing in their gametes.
The Chlamydiota are a bacterial phylum and class whose members are remarkably diverse, including pathogens of humans and animals, symbionts of ubiquitous protozoa, and marine sediment forms not yet well understood. All of the Chlamydiota that humans have known about for many decades are obligate intracellular bacteria; in 2020 many additional Chlamydiota were discovered in ocean-floor environments, and it is not yet known whether they all have hosts. Historically it was believed that all Chlamydiota had a peptidoglycan-free cell wall, but studies in the 2010s demonstrated a detectable presence of peptidoglycan, as well as other important proteins.
The Rhodobacteraceae are a family of Pseudomonadota in the order Rhodobacterales within the alpha subgroup. Like all Pseudomonadota, they are gram-negative. It contains chemoorganotrophs and photoheterotrophs bacteria. Many occur in aquatic habitats.
The Eubacteriales are an order of bacteria placed within the class Clostridia.
The Syntrophobacterales are an order of Thermodesulfobacteriota. All genera are strictly anaerobic. Many of the family Syntrophobacteraceae are sulfate-reducing. Some species are motile by using one polar flagellum.
The Thermodesulfobacteriota are a phylum of thermophilic sulfate-reducing bacteria.
The Myxococcota are a phylum of bacteria known as the fruiting gliding bacteria. All species of this group are Gram-negative. They are predominantly aerobic genera that release myxospores in unfavorable environments.
The Nitrosopumilales are an order of the Archaea class Nitrososphaeria.
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photosynthesis ; and anaerobic halorespirers, which uses halogenated organics as electron acceptors.
Nitrospirota is a phylum of bacteria. It includes multiple genera, such as Nitrospira, the largest. The first member of this phylum, Nitrospira marina, was discovered in 1985. The second member, Nitrospira moscoviensis, was discovered in 1995.
The phylum Elusimicrobiota, previously known as "Termite Group 1", has been shown to be widespread in different ecosystems like marine environment, sewage sludge, contaminated sites and soils, and toxic wastes. The high abundance of Elusimicrobiota representatives is only seen for the lineage of symbionts found in termites and ants.
Nanohaloarchaea is a clade of diminutive archaea with small genomes and limited metabolic capabilities, belonging to the DPANN archaea. They are ubiquitous in hypersaline habitats, which they share with the extremely halophilic haloarchaea.
The "Aigarchaeota" are a proposed archaeal phylum of which the main representative is Caldiarchaeum subterraneum. It is not yet clear if this represents a new phylum or a Nitrososphaerota order, since the genome of Caldiarchaeum subterraneum encodes several Nitrososphaerota-like features. The name "Aigarchaeota" comes from the Greek αυγή, avgí, meaning "dawn" or "aurora", for the intermediate features of hyperthermophilic and mesophilic life during the evolution of its lineage.
Atribacterota is a phylum of bacteria, which are common in anoxic sediments rich in methane. They are distributed worldwide and in some cases abundant in anaerobic marine sediments, geothermal springs, and oil deposits. Genetic analyzes suggest a heterotrophic metabolism that gives rise to fermentation products such as acetate, ethanol, and CO2. These products in turn can support methanogens within the sediment microbial community and explain the frequent occurrence of Atribacterota in methane-rich anoxic sediments. According to phylogenetic analysis, Atribacterota appears to be related to several thermophilic phyla within Terrabacteria or may be in the base of Gracilicutes. According to research, Atribacterota shows patterns of gene expressions which consists of fermentative, acetogenic metabolism. These expressions let Atribacterota to be able to create catabolic and anabolic functions which are necessary to generate cellular reproduction, even when the energy levels are limited due to the depletion of dissolved oxygen in the areas of sea waters, fresh waters, or ground waters.
The candidate phyla radiation is a large evolutionary radiation of bacterial lineages whose members are mostly uncultivated and only known from metagenomics and single cell sequencing. They have been described as nanobacteria or ultra-small bacteria due to their reduced size (nanometric) compared to other bacteria.
The Genome Taxonomy Database (GTDB) is an online database that maintains information on a proposed nomenclature of prokaryotes, following a phylogenomic approach based on a set of conserved single-copy proteins. In addition to resolving paraphyletic groups, this method also reassigns taxonomic ranks algorithmically, updating names in both cases. Information for archaea was added in 2020, along with a species classification based on average nucleotide identity. Each update incorporates new genomes as well as automated and manual curation of the taxonomy.