Actinomycetales

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Actinomycetales
Actinomyces naeslundii

Actinomyces naeslundii

Systematics
Classification : Creature
Domain : Bacteria (bacteria)
Department : Actinobacteria
Class : Actinobacteria
Order : Actinomycetales
Scientific name
Actinomycetales
Buchanan in 1917 emend. Zhi et al. 2009

The Actinomycetales form an order of bacteria within the class of Actinobacteria . The Actinomycetales are gram positive and have a high GC content . The proportion of these nucleobases guanine and cytosine in the DNA is used to subdivide ( taxonomy ) gram-positive bacteria into the two classes Actinobacteria and Firmicutes . In contrast to Actinobacteria, the latter have a low GC content.

Bacteria of this order were previously called Actinomycetes , German radiation fungi , because they were considered fungi due to their partially extensive mycelia . Some families are very species-rich and play an important role in nature, others are pathogenic for humans and animals.

features

Light microscope picture of a Streptomyces species, with branched filaments that make up the mycelium and with chains of spherical spores.
Light microscope picture of a type of Dermatophilus showing a cluster of irregularly shaped cells.

Many representatives of the Actinomycetales are aerobic (e.g. the genera Arthrobacter , Corynebacterium , Micrococcus , Mycobacterium , Nocardia , Streptomyces ), but there are also species that grow facultatively anaerobic or strictly anaerobic . Many actinomycetales form spores . An important feature of many Actinomycetales is the formation of filaments . These elongated and branched cells form plexuses, which are also known as mycelium . The name actinomycetes ( ray fungi ) refers to the radiating structure of the bulbous colonies of pathogenic Actinomyces species in the tissue of infected animals.

The formation of mycelia is u. a. typical of the genera Streptomyces , Nocardia and Actinomyces . As with mushrooms, a distinction can be made between aerial mycelium and substrate mycelium. The substrate mycelium develops in the nutrient medium , while the aerial mycelium is formed from cells that grow in the gas space above the nutrient medium and often form spores. The filamentous cells of the facultative anaerobic genus Dermatophilus divide transversely and in several planes, creating clusters of coccal-shaped , mobile cells. An aerial mycelium is not formed.

Not all species form mycelia, in some cases the plexuses only appear in certain growth phases. So is z. B. the species Mycobacterium bovis more or less rod-shaped , Arthrobacter forms cocci or rod-shaped cells. The term Coryneforme is common for the club-shaped shape of the cells of Corynebacterium and related bacteria .

The Actinomycetales can (besides the taxonomic classification) be divided into different groups depending on the characteristic. One possibility is the division into obligatory aerobic (oxidative actinomycetes) and species that are able to grow even without oxygen through a fermentative metabolism, i.e. anaerobically. The latter is mainly found in the Actinomycetaceae family , e.g. B. the genera Actinomyces and Arcanobacterium . The facultative anaerobes mainly inhabit the mucous membranes of animals and humans, while the obligatory aerobes mostly occur in the free environment.

meaning

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

The genus Mycobacterium contains, among other things, the causative agent of tuberculosis (especially Mycobacterium tuberculosis ) and the causative agent of leprosy , Mycobacterium leprae . The causative agent of diphtheria is Corynebacterium diphtheriae . Micrococcus species are found in test materials of human and animal origin either as contaminants, commensals or, in rare cases (e.g. in people with weakened immune systems), also as infectious agents.

Further, more or less low 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 .

Dermatophilus congolensis from the Dermatophilaceae familycauses dermatophilosis , an acute inflammation of the skin in cattle, sheep, horses and occasionally also in humans.

The apathogenic, ecologically important representatives include z. B. the genus Frankia , a nitrogen fixer with plants - z. B. with alders - enters into a symbiosis. Frankia supplies the plant with nitrogen compounds, in return the bacterium benefits from the nutrients produced by the plant. Frankia is aerobic. Cellulomonas is also of ecological importance , representatives of this genus can utilize cellulose and are thus involved in the breakdown of dead plant material. Nocardia species can be found in the soil, where they break down numerous organic compounds that most bacteria cannot use, such as: B. hydrocarbons .

Systematics

External system

The very species-rich order Actinomycetales forms together with the order Bifidobacteriales the subclass Actinobacteridae, one of several subclasses in the class Actinobacteria in the Phylum Actinobacteria . Important representatives for human medicine can be found in the two orders of the Bifidobacteriales and Actinomycetales.

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

Internal system

In addition to some isolates that are not classified with certainty, the order Actinomycetales includes the following suborders and families (as of 2013):

Remarks

  1. In 2009 it was proposed to combine the Gordoniaceae and Nocardiaceae families into the expanded Nocardiaceae family.
  2. Since 1999, several new types of bacteria have been discovered that have been assigned to the newly described genus Williamsia . According to the current systematics of bacteria, this genus belongs to the Nocardiaceae family, in other sources it is included in the new Williamsiaceae family.
  3. The representatives of the Yaniellaceae family, newly discovered at the beginning of the 21st century, are all representatives of the Micrococcaceae family and are listed there as the new genera Yaniella and Enteractinococcus .
  4. In 2011, it was proposed to combine the Actinosynnemataceae and Pseudonocardiaceae families into the extended family Pseudonocardiaceae.

etymology

The generic name and thus the ordinal name (with the usual suffix -ales) can be traced back to the appearance of the bacteria ( ancient Greek actinos , "rays" and ancient Greek mukês , "mushroom"). Actinomyces can therefore be translated as radiation fungus, because so-called drusen form in the tissue of cattle suffering from actinomycosis , these have a radiation-like structure. The external similarity of the bacterial cultures with the mycelia formed by fungi led to the fact that they were initially mistaken for fungi.

Selection of some genera

swell

literature

Individual evidence

  1. ^ A b c d Hans G. Schlegel, Christiane Zaborosch: General microbiology . 7th edition. Thieme Verlag, Stuttgart / New York 1992, ISBN 3-13-444607-3 , p. 101-108 .
  2. ↑ a b Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel, 1st edition. Spektrum Akademischer Verlag GmbH, Heidelberg / Berlin 2000, ISBN 978-3-8274-0566-1 , pp. 572-582.
  3. ^ A b Jean Euzéby, Aidan C. Parte: Phylum "Actinobacteria". In: List of Prokaryotic names with Standing in Nomenclature Systematics of Bacteria (LPSN) . Retrieved December 19, 2013 .
  4. ^ A b Jean Euzéby, Aidan C. Parte: Order Actinomycetales. In: List of Prokaryotic names with Standing in Nomenclature Systematics of Bacteria (LPSN) . Retrieved December 20, 2013 .
  5. ↑ a b XY Zhi, WJ Li, E. Stackebrandt: An update of the structure and 16S rRNA gene sequence-based definition of higher ranks of the class Actinobacteria, with the proposal of two new suborders and four new families and emended descriptions of the existing higher taxa. In: International journal of systematic and evolutionary microbiology. Volume 59, No. 3, March 2009, pp. 589-608, ISSN  1466-5026 . doi: 10.1099 / ijs.0.65780-0 . PMID 19244447 .
  6. ^ Taxonomy Browser Williamsiaceae. In: National Center for Biotechnology Information (NCBI) website . Retrieved December 20, 2013 .
  7. ^ AF Yassin, H. Hupfer, C. Siering, HP Klenk, P. Schumann: Auritidibacter ignavus gen. Nov., Sp. nov., of the family Micrococcaceae isolated from an ear swab of a man with otitis externa, transfer of the members of the family Yaniellaceae Li et al. 2008 to the family Micrococcaceae and emended description of the suborder Micrococcineae. In: International journal of systematic and evolutionary microbiology. Volume 61, No. 2, February 2011, pp. 223-230, ISSN  1466-5034 . doi: 10.1099 / ijs.0.019786-0 . PMID 20190019 .
  8. ↑ DP Labeda, M. Goodfellow, J. Chun, XY Zhi, WJ Li: Reassessment of the systematics of the suborder Pseudonocardineae: transfer of the genera within the family Actinosynnemataceae Labeda and Kroppenstedt 2000 emend. Zhi et al. 2009 into an emended family Pseudonocardiaceae Embley et al. 1989 emend. Zhi et al. 2009. In: International journal of systematic and evolutionary microbiology. Volume 61, No. 6, June 2011, pp. 1259-1264, ISSN  1466-5034 . doi: 10.1099 / ijs.0.024984-0 . PMID 20601483 .

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