The Actinomycetota are a diverse phylum of Gram-positive bacteria with high GC content. They can be terrestrial or aquatic. They are of great importance to land flora because of 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, as fungi do, 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.
Nanoarchaeota is a proposed phylum in the domain Archaea that currently has only one representative, Nanoarchaeum equitans, which was discovered in a submarine hydrothermal vent and first described in 2002.
Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture.
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 verrucomicrobial bacterium Akkermansia muciniphila is a human intestinal symbiotic bacterium that is considered as a promising probiotic.
The Thermomicrobia is a group of thermophilic green non-sulfur bacteria. Based on species Thermomicrobium roseum and Sphaerobacter thermophilus, this bacteria class has the following description:
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.
Fibrobacterota is a small bacterial phylum which includes many of the major rumen bacteria, allowing for the degradation of plant-based cellulose in ruminant animals. Members of this phylum were categorized in other phyla. The genus Fibrobacter was removed from the genus Bacteroides in 1988.
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.
The Nitrososphaerota are a phylum of the Archaea proposed in 2008 after the genome of Cenarchaeum symbiosum was sequenced and found to differ significantly from other members of the hyperthermophilic phylum Thermoproteota. Three described species in addition to C. symbiosum are Nitrosopumilus maritimus, Nitrososphaera viennensis, and Nitrososphaera gargensis. The phylum was proposed in 2008 based on phylogenetic data, such as the sequences of these organisms' ribosomal RNA genes, and the presence of a form of type I topoisomerase that was previously thought to be unique to the eukaryotes. This assignment was confirmed by further analysis published in 2010 that examined the genomes of the ammonia-oxidizing archaea Nitrosopumilus maritimus and Nitrososphaera gargensis, concluding that these species form a distinct lineage that includes Cenarchaeum symbiosum. The lipid crenarchaeol has been found only in Nitrososphaerota, making it a potential biomarker for the phylum. Most organisms of this lineage thus far identified are chemolithoautotrophic ammonia-oxidizers and may play important roles in biogeochemical cycles, such as the nitrogen cycle and the carbon cycle. Metagenomic sequencing indicates that they constitute ~1% of the sea surface metagenome across many sites.
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.
Bacterial phyla constitute the major lineages of the domain Bacteria. While the exact definition of a bacterial phylum is debated, a popular definition is that a bacterial phylum is a monophyletic lineage of bacteria whose 16S rRNA genes share a pairwise sequence identity of ~75% or less with those of the members of other bacterial phyla.
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.
Gordonia is a genus of gram-positive, aerobic, catalase-positive bacterium in the Actinomycetota, closely related to the Rhodococcus, Mycobacterium, Skermania, and Nocardia genera. Gordonia bacteria are aerobic, non-motile, and non-sporulating. Gordonia is from the same lineage that includes Mycobacterium tuberculosis. The genus was discovered by Tsukamura in 1971 and named after American bacteriologist Ruth Gordon. Many species are often found in the soil, while other species have been isolated from aquatic environments. Some species have been associated with problems like sludge bulking and foaming in wastewater treatment plants. Gordonia species are rarely known to cause infections in humans.
DPANN is a superphylum of Archaea first proposed in 2013. Many members show novel signs of horizontal gene transfer from other domains of life. They are known as nanoarchaea or ultra-small archaea due to their smaller size (nanometric) compared to other archaea.
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.
TM7x, also known as Nanosynbacter lyticus type strain TM7x HMT 952. is a phylotype of one of the most enigmatic phyla, Candidatus Saccharibacteria, formerly candidate phylum TM7. It is the only member of the candidate phylum that has been cultivated successfully from the human oral cavity, and stably maintained in vitro. and serves as a crucial paradigm. of the newly described Candidate Phyla Radiation (CPR). The cultivated oral taxon is designated as Saccharibacteria oral taxon TM7x. TM7x has a unique lifestyle in comparison to other bacteria that are associated with humans. It is an obligate epibiont parasite, or an "epiparasite", growing on the surface of its host bacterial species Actinomyces odontolyticus subspecies actinosynbacter strain XH001, which is referred to as the "basibiont". Actinomyces species are one of the early microbial colonizers in the oral cavity. Together, they exhibit parasitic epibiont symbiosis.
Modulibacteria(Moduliflexota) is a bacterial phylum formerly known as KS3B3 or GN06. It is a candidate phylum, meaning there are no cultured representatives of this group. Members of the Modulibacteria phylum are known to cause fatal filament overgrowth (bulking) in high-rate industrial anaerobic wastewater treatment bioreactors.
NC10 is a bacterial phylum with candidate status, meaning its members remain uncultured to date. The difficulty in producing lab cultures may be linked to low growth rates and other limiting growth factors.
