The Actinobacteria are a phylum of Gram-positive bacteria. 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, Actinobacteria 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 actinobacteria 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.
Deinococcus–Thermus is a phylum of bacteria 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. Cavalier-Smith calls this clade Hadobacteria.
The Aurantimonadaceae are a small family of marine bacteria. Six species are known. Aurantimonas coralicida causes a white plague in corals. Fulvimarina pelagi was isolated from seawater, and takes the form of nonmotile rods.
The Frankineae are a suborder of the Actinomycetales order. Like all Actinobacteria, the species are Gram-positive with high G+C ratios.
The Coriobacteriaceae are a family of Actinobacteria, given their own subclass (Coriobacteridae). The family Coriobacteriaceae has been shown to increase significantly in the ceca of mice in response to stress.
Rubrobacter is a genus of Actinobacteria, given its own subclass (Rubrobacteridae). It is radiotolerant and may rival Deinococcus radiodurans in this regard.
The Micrococcineae are a suborder of bacteria of the order Actinomycetales. They are Gram-positive soil organisms, and are also paraphyletic with respect to the suborder Actinomycetineae and order Bifidobacteriales, i.e. the Actinomycetineae and Bifidobacteriales are both nested within the clade Micrococcineae.
The Pseudonocardiaceae are a family of bacteria in the order Actinomycetales and the only member of the suborder Pseudonocardineae.
The Jiangellaceae are the only family of the order Jiangellales, which is a part of the Actinobacteria.
The Thermoleophilia are a newly proposed class of Actinobacteria that was created from the splitting of the Rubrobacteridae, due to its phylogenetic branching order.
The Glycomycetaceae are the only family of the suborder Glycomycetales, which is a part of Actinobacteria.
The Catenulisporineae comprise a suborder of Actinomycetales with two monotypic families.
The Nakamurellaceae are an actinomycete family within the highly polyphyletic suborder Frankineae.
The Kineosporiaceae comprise a polyphyletic Actinomycete family, sole member of the order Kineosporiales.
Propionibacterineae is an Actinomycete suborder with two families and numerous genera.
Streptosporangineae is a suborder of bacteria in the order Actinomycetales.
Rubrobacteria is one of five classes of Actinobacteria that contain one order, one family, one genus, and seven species.
The Thermoleophilia are a newly proposed class of Actinobacteria that was created from the splitting of the Rubrobacteridae, due to its phylogenetic branching order.
The Acidimicrobiia are a class of Actinobacteria, in which three families, eight genera, and nine species have been described, Acidimicrobium ferrooxidans is the type species of the order.
