Actinomyces naeslundii

The Actinomycetales constitute an order of bacteria within the class of Actinobacteria. The Actinomycetales are gram- positive and have a high GC content. The term " GC-content " refers to the percentage of DNA guanine and cytosine bases in the DNA, and is used for the subdivision ( the taxonomy ) gram-positive bacteria in the two classes of Firmicutes and Actinobacteria. The latter have a low GC content, in contrast to the Actinobacteria.

The unspecified term actinomycetes is also used for the order Actinomycetales and can be translated as actinomycetes, since you have the bacteria previously treated as fungi. Some families are very rich in species and play an important role in nature, others are pathogenic for humans and animals.

  • 5.1 Literature
  • 5.2 Notes and references


Many members of the Actinomycetales are aerobic (eg the genera Arthrobacter, Corynebacterium, Micrococcus, Mycobacterium, Nocardia, Streptomyces ), but there are also species from growing facultative anaerobes or strict anaerobes. Many Actinomycetales form spores. An important feature of many Actinomycetales is the formation of filaments. These elongated and branched cells form fencing, which are also known as the mycelium. The name of actinomycetes ( Actinomyces ) refers to the radiating structure of the tuberous colonies of pathogenic Actinomyces species in tissues of infected animals.

The formation of mycelia is, inter alia, typical of the genus Streptomyces, Nocardia and Actinomyces. It can be different as with the mushrooms, substrate mycelium and aerial mycelium between. The substrate mycelium develops in the culture medium, while the aerial mycelium is formed from cells that grow above the nutrient medium into the gas space and often form spores. The filamentous cells of the facultative anaerobic species Dermatophilus sharing across and in many layers, and develop clusters (cluster ) of coccoid, motile cells. An aerial mycelium is not formed.

Not all species form mycelia, some part of the braids only in certain growth phases. For example, the genus Mycobacterium bovis is more or less rod-shaped, Arthrobacter forms coccus or rod-shaped cells. For the club- like shape of the cells of Corynebacterium and related bacteria coryneform the name is familiar.

The Actinomycetales can be divided into different groups depending on the feature (in addition to the taxonomic classification ). One possibility is the division into obligate aerobic (oxidative actinomycetes ) and species that are able, even without oxygen by a fermentative metabolism, so to grow anaerobically. The latter are mainly found in the family of Actinomycetaceae, for example the genera Actinomyces and Arcanobacterium. The facultative anaerobes mainly inhabit the mucous membranes of animals and humans, while the obligate aerobes usually occur in the external environment.


In human medicine, only a few representatives of play ( relative to the total number of species ) play an important role, most species are not pathogenic ( non-pathogenic ). Some types (e.g., those of the genera Streptomyces and Amycolatopsis ) can be used for the production of antibiotics. The pathogenic species include, for example the genera Actinomyces ( Actinomycetaceae, cause of Aktinomykosen ), and Nocardia ( Nocardiaceae, triggers of Nocardiosen ).

The genus Mycobacterium contains, among other things, the causative agent of tuberculosis ( esp. Mycobacterium tuberculosis ) and the causative agent of leprosy, Mycobacterium leprae. The causative agent of diphtheria is Corynebacterium diphtheriae. Micrococcus species are found in specimens of human and animal origin, either as contaminants or commensals in rare cases (eg, in immune -compromised ) as infectious agents.

More, more or less weakly pathogenic genera and species are of medical importance: Mobiluncus ( Actinomycetaceae ) at vaginosis, Propionibacterium ( Propionibacteriaceae ) in endocarditis, Rhodococcus equi ( Nocardiaceae ) in infections of the respiratory tract, Corynebacterium xerosis ( Corynebacteriaceae ) in endocarditis, Tsukamurella ( Tsukamurellaceae ) in meningitis.

Among the non-pathogenic, ecologically important representatives include, for example, the genus Frankia, a nitrogen fixers, which with plants - a symbiosis received - for example, with alders. Frankia provides the plant nitrogen compounds, in turn, benefits the bacterium by the produced by the plant nutrients. Frankia is aerobic. Also of ecological importance is Cellulomonas, members of this genus can utilize cellulose and are therefore involved in the breakdown of dead plant material. Nocardia species are found in the soil, where they degrade numerous organic compounds that can not be used by most bacteria, such as hydrocarbons.


Outer systematics

The very species-rich order Actinomycetales, together with the order Bifidobacteriales the subclass Actinobacteridae, one of several sub-classes in the class Actinobacteria in the phylum Actinobacteria. Important representatives for human medicine are to be found in the two orders of Bifidobacteriales and Actinomycetales.

The order Actinomycetales Buchanan et al. 1917 emend. Zhi et al. 2009 is the order of the subclass type Actinobacteridae. The genus Actinomyces is the type genus of the order.

Inside systematics

In addition to some not safely disposed isolates belong to the order Actinomycetales following sub- orders and families (as of 2013):

  • Subordination Actinomycineae Stackebrandt et al. 1997 Actinomycetaceae
  • Actinopolysporaceae
  • Actinospicaceae - Catenulisporaceae
  • Corynebacteriaceae - Dietziaceae - Gordoniaceae ( see Note 1) - Mycobacteriaceae - Nocardiaceae ( see Note 1) - Segniliparaceae - Tsukamurellaceae - " Williamsiaceae " (see Note 2 )
  • Acidothermaceae - Cryptosporangiaceae - Frankiaceae - Geodermatophilaceae - Nakamurellaceae - Sporichthyaceae
  • Glycomycetaceae
  • Jiangellaceae
  • Kineosporiaceae
  • Beutenbergiaceae - Bogoriellaceae - Brevibacteriaceae - Cellulomonadaceae - Demequinaceae - Dermabacteraceae - Dermacoccaceae - Dermatophilaceae - Intrasporangiaceae - Jonesiaceae - Microbacteriaceae - Micrococcaceae (see Note 3 ) - Promicromonosporaceae - Rarobacteraceae - Ruaniaceae - Sanguibacteraceae
  • Micromonosporaceae
  • Nocardioidaceae - Propionibacteriaceae
  • Actinosynnemataceae ( see note 4) - Pseudonocardiaceae ( see note 4)
  • Nocardiopsaceae - Streptosporangiaceae - Thermomonosporaceae



The genus name, and thus the order name suggests ( with the usual suffix for ales ) are due to the appearance of the bacteria (Greek aktinos, "rays" and Greek Mukes, "mushroom" ). Actinomyces can therefore be translated with actinomycete, because suffering from actinomycosis cattle form in the tissues called the Druze, they have a beam -like structure. The external similarity of the bacterial cultures with the mycelia of fungi formed meant that they were considered initially for fungi.

Selection of some genera

  • Actinomyces
  • Amycolatopsis
  • Arcanobacterium
  • Arthrobacter
  • Brevibacterium
  • Cellulomonas
  • Corynebacterium
  • Frankia
  • Gordonia
  • Micrococcus
  • Mycobacterium
  • Nocardia
  • Propionibacterium
  • Rhodococcus
  • Streptomyces