Quick Facts Scientific classification, Type genus ...

Acidobacteriota
Acidobacterium cf. capsulatum
Scientific classification
Domain:	Bacteria
Phylum:	Acidobacteriota Thrash and Coates 2021[1]
Type genus
Acidobacterium Kishimoto et al. 1991
Classes[2]
"Acidobacteriia" Blastocatellia "Ca. Guanabacteria" Holophagae "Ca. Polarisedimenticolia" Thermoanaerobaculia Vicinamibacteria
Synonyms
"Acidobacteria" Thrash and Coates 2010[3] "Acidobacteraeota" Oren et al. 2015 "Acidobacteriota" Whitman et al. 2018

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Acidobacteriota is a phylum of Gram-negative bacteria. Its members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture.^[4][5][6]

Members of this phylum are physiologically diverse, and can be found in a variety of environments including soil, decomposing wood,^[7] hot springs, oceans, caves, and metal-contaminated soils.^[8] The members of this phylum are particularly abundant in soil habitats representing up to 52% of the total bacterial community.^[9] Environmental factors such as pH and nutrients have been seen to drive Acidobacteriota dynamics.^[10][11][12] Many Acidobacteriota are acidophilic, including the first described member of the phylum, Acidobacterium capsulatum.^[13]

There is much that is unknown about Acidobacteria both in their form and function. Thus, this is a growing field of microbiology. Some of this uncertainty can be attributed to the difficulty with which these bacteria are grown in the laboratory. There has been recent success in propagation by using low concentrations of nutrients in combination with high amounts of CO₂,^[10] yet, progress is still quite slow. These new methods have only allowed approximately 30% of subdivisions to have species documented.^[10]

Additionally, many of the samples sequenced do not have taxonomic names as they have not yet been fully characterized. This area of study is a very current topic, and scientific understanding is expected to grow and change as new information comes to light.

Other notable species are Holophaga foetida,^[14] Geothrix fermentans,^[15] Acanthopleuribacter pedis^[16] and Bryobacter aggregatus.^[17] Since they have only recently been discovered and the large majority have not been cultured, the ecology and metabolism of these bacteria is not well understood.^[5] However, these bacteria may be an important contributor to ecosystems, since they are particularly abundant within soils.^[18] Members of subdivisions 1, 4, and 6 are found to be particularly abundant in soils.^[19]

As well as their natural soil habitat, unclassified subdivision 2 Acidobacteriota have also been identified as a contaminant of DNA extraction kit reagents, which may lead to their erroneous appearance in microbiota or metagenomic datasets.^[20]

Members of subdivision 1 have been found to dominate in low pH conditions.^[21][10] Additionally, Acidobacteriota from acid mine drainage have been found to be more adapted to acidic pH conditions (pH 2-3) compared to Acidobacteriota from soils,^[22] potentially due to cell specialization and enzyme stability.^[10]

The G+C content of Acidobacteria genomes are consistent within their subdivisions - above 60% for group V fragments and roughly 10% lower for group III fragments.^[5]

The majority of Acidobacteriota are considered aerobes.^[23][24] There are some Acidobacteriota that are considered anaerobes within subdivision 8^[15] and subdivision 23.^[25] It has been found that some strains of Acidobacteriota originating from soils have the genomic potential to respire oxygen at atmospheric and sub-atmospheric concentrations.^[24]

Members of the Acidobacteriota phylum have been considered oligotrophic bacteria due to high abundances in low organic carbon environments.^[10] However, the variation in this phylum may indicate that they may not have the same ecological strategy.^[10]

The first species, Acidobacterium capsulatum, of this phylum was discovered in 1991.^[26] However, Acidobacteriota were not recognized as a distinct clade until 1997,^[13] and were not recognized as a phylum until 2012.^[27] First genome was sequenced in 2006.^[28]

In an effort to further classify Acidobacteria, 16S rRNA gene regions were sequenced from many different strains. These sequences lead to the formation of subdivisions within the phyla. Today, there are 26 accepted subdivisions recognized in the Ribosomal Database Project.^[10]

Much of this variety comes from populations of acidobacteria found in soils contaminated with uranium. Therefore, most of the known species in this phyla are concentrated in a few of the subdivisions, the largest being #1. Most of these microbes are aerobes, and they are all heterotrophic. Subdivision 1 contains 11 of the known genera in addition to the majority of the species that have been able to be cultivated thus far.^[10]

Within the 22 known genera, there are 40 conclusive species. The genera are divided amongst subdivisions 3, 4, 8, 10, 23, and 1. As the Acidobateria are a developing area of microbiology, it is hypothesized that these numbers will change drastically with further study.^[10]

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature^[2] and National Center for Biotechnology Information.^[33]

• List of bacterial orders
• List of bacteria genera