Actinobacteria

from Wikipedia, the free encyclopedia
Actinobacteria
Bifidobacterium adolescentis stained according to Gram, light microscopy

Bifidobacterium adolescentis stained
according to Gram , light microscopy

Systematics
Classification : Creature
Domain : Bacteria (bacteria)
Department : Actinobacteria
Class : Actinobacteria
Scientific name of the  department
Actinobacteria
Cavalier-Smith 2002
Scientific name of the  class
Actinobacteria
Stackebrandt et al. 1997

The actinobacteria form one of the most biodiverse divisions ( divisio , also called phyla among prokaryotes ) within the domain of bacteria . As " Germanized " notation, the names will Actinobacteria and Actinobacteria . Together with the Firmicutes , they form the large group of gram-positive bacteria. A distinguishing feature is that the representatives of the Actinobacteria have a rather high content of the DNA bases guanine and cytosine in their DNA . However, this addition to the definition is not always applicable. The Actinobacteria phylum currently (as of 2018) contains five other classes in addition to the Actinobacteria class of the same name . The systematics of the Actinobacteria class has changed significantly in recent years due to the use of phylogenetic methods, with which the tribal history and the relationships between the bacteria are clarified. Currently (as of 2018) the class Actinobacteria contains nine orders , including the Actinomycetales .

features

Appearance

Colonies of Actinobacteria in slanted agar tubes, here Actinomadura madurae forms white, Nocardia asteroides yellow and Micromonospora species red colonies (from left to right).

The Actinobacteria are gram-positive bacteria. Their cells can be rod- shaped or cocci or coryne-shaped . Some representatives are filamentous and multicellular, many can form endospores . Together with the Firmicutes they form the large group of gram-positive bacteria. The cells grow into visible colonies on suitable nutrient media . Many representatives of the Actinobacteria stand out because their colonies do not look smooth but wrinkled.

Chemotaxonomic Features

Actinobacteria are bacteria with a high GC content , i.e. a high proportion of nucleobases ( guanine and cytosine ) in the bacterial DNA . Specifically, this means a GC content of more than 55  mol percent . This applies to the majority of the representatives, but not to all, so that this definition alone is not sufficient.

Growth and metabolism

Actinobacteria have diverse metabolic pathways , only photosynthetically active representatives are not known. Some metabolic pathways are restricted to Actinobacteria and are not found in other prokaryotes . The metabolism of most representatives of Actinobacteria can be characterized as chemoorganotrophic and heterotrophic , they use organic compounds as a source of energy and also to build up cellular substances. They either use aerobic respiration to break down the substrates or carry out fermentation . Accordingly, their behavior to the oxygen contained in the air can vary: The representatives can grow strictly aerobically , facultatively anaerobically , microaerophilically or strictly anaerobically .

Actinobacteria are also exceptional in terms of certain metabolic products . For example, representatives of the Mycobacteriaceae family (Mycobacteria) have a high proportion of lipids in the peptidoglycan of the bacterial cell wall . The mycolic acids contained in it are a peculiarity of some families within the class of Actinobacteria and lead to the fact that the cell wall is hydrophobic , which is also known as acid-resistant cell wall . The synthesis of these lipids is also unusual, involving enzyme complexes known as polyketide synthases .

Structural formula of mycothiol

A specialty of Actinobacteria is the production of mycothiol instead of glutathione . Mycothiol not subject to the degree of auto-oxidation , as is the case with glutathione. It acts as an anti-oxidant for the amino acid cysteine . Two cysteine ​​residues can form a disulfide bridge with one another , which is involved in the formation of the tertiary and quaternary structure in proteins . Furthermore, because of the thiol group it contains, mycothiol serves as a supply of thiol, which helps to maintain a reducing environment within the cell and thus to protect against oxidative stress .

The Streptomycetaceae family with the genus Streptomyces are another interesting example from the Phylum Actinobacteria, as they are known for unusual metabolic pathways. They also produce a wide range of secondary products, such as antibiotics and geosmines , which cause the typical earth odor.

Occurrence and meaning

Actinobacteria are widespread in the environment, soils and water are typical habitats . Among the Actinobacteria there are numerous representatives that break down pollutants and complex compounds in nature or play an important role as symbionts or pathogens . Examples are species from the genera Mycobacterium and Actinomyces .

Systematics

Historical development

The systematics of Actinobacteria and the representatives included has changed several times. From the generic name Actinomyces , which Corda used in 1839 for the bacterial species Actinomyces bovis , which was discovered in cattle, the name actinomycetes, a not clearly defined group of morphologically similar microorganisms, developed . The generic names of the representatives were also subject to numerous changes. In the case of the actinomycetes, formerly known as radiation fungi, this may be the case. a. that although they are bacteria, they are similar in appearance to fungi . The generic name Streptomyces ( Waksman and Henrici 1943) combines the names Streptothrix and Actinomyces first used for the group .

From the first not clearly defined group of actinomycetes developed the order of the Actinomycetales that of Buchanan described the 1917th In the 1950s and 1960s, numerous new species were discovered, which were known as sporoactinomycetes and coryneforms and which were similar to the actinomycetes. However, the known representatives showed a broad phenotypic heterogeneity, so that the non-uniform systems for classification made a taxonomic classification difficult. This was improved in the 1980s by the internationally coordinated systematics of bacteria . In addition to morphological and biochemical , chemotaxonomic features were increasingly used for the classification. Although this made the assignment to a genus easier, it led to higher taxa (such as the order or class) appearing as a non-uniformly composed group.

In the 1990s, in addition to the order Actinomycetales, the class Actinomycetes was also listed, an assignment of other gram-positive bacteria with a high GC content only on the basis of morphological and chemotaxonomic characteristics became increasingly difficult. The ability to carry out genetic investigations (e.g. DNA sequencing ) brought new insights into the systematics of bacteria and helped to elucidate the tribal history and the relationships between the microorganisms ( phylogenetic tree ). In the case of bacteria, this applies in particular to the investigation of 16S rRNA, a typical representative of ribosomal RNA for prokaryotes . Based on these results, Stackebrandt et al. 1997 introduced a new classification system. The class Actinobacteria was introduced with the Actinobacteridae as a subclass .

For the molecular-phylogenetic tree construction, Zhi, Li and Stackebrand used the Neighbor Joining , the Maximum Parsimony and the Maximum Likelihood analysis methods. In doing so, they established patterns of signature nucleotides of the 16S rRNA (English “patterns of 16S rRNA signature nucleotides”), which define the higher taxa (family to subclass). The position of the nucleotide in the rRNA and which nucleotide - abbreviated by the nucleobases it contains , namely adenine (A), guanine (G), cytosine (C) and uracil (U) - is given is indicated . The discovery of new species and their assignment to new genera made it necessary to adapt the pattern of signature nucleotides to the 16S rRNA. In 2009 this led to an “update” of the definition of the higher taxa in the class Actinobacteria by Zhi et al. The taxa subclass and subordination were also used here.

These two approaches were included in 2012 in the 2nd edition of Bergey's Manual of Systematic Bacteriology , the standard work for the systematics of bacteria. The subclasses were raised to classes and the subordinates to orders. The new system also includes that similar taxon groups were combined into one or, conversely, that a taxon group was divided if its members were too different, or that genera were placed in a different family.

"It is not the 'truth', but an attempt to bring rational order to a group of related organisms, at least for the time being."

"It is not the 'truth', but an attempt to bring a reasonable order into a group of related organisms, at least for the time being."

- X.-Y. Zhi, W.-J. 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. 2009.

Current system

In the current system, the subclasses are dispensed with and the number of subordinates has been reduced. In addition, the phylum of Actinobacteria was introduced by Cavalier-Smith in 2002 as a superordinate taxon.

Currently (as of 2018) the class Actinobacteria contains nine orders, the Acidothermales, the Actinomycetales, the Bifidobacteriales, the Frankiales, the Geodermatophilales, the Kineosporiales, the Micrococcales, the Nakamurellales and the Nitriliruptorales. According to the concept laid down in the 2nd edition of Bergey's Manual of Systematic Bacteriology 2012, numerous other orders are added that were previously subordinate to the Actinomycetales, such as the "Corynebacteriales" (Corynebacterineae). However, the authors characterize these cases as a preliminary assessment. Thus the species-rich order Actinomycetales (see there) remains initially divided into several sub-orders. Numerous known representatives of Actinobacteria are included in this order, for example in the suborder Actinomycineae the family Actinomycetaceae (with the type genus Actinomyces ), the Streptomycetaceae in the suborder Streptomycineae and the Corynebacteriaceae , the Mycobacteriaceae and the Nocardiaceae in the suborder Corynebaceae.

In describing the class Actinobacteria Stackebrandt et al. In 1997 it was neglected to define a nomenclature type that forms the basis for defining and naming a higher-level taxon. According to the rules of the International Code of Nomenclature of Bacteria , the taxon is actually inadmissible. This faux pas is mentioned in the 2nd edition of Bergey's Manual of Systematic Bacteriology , but nevertheless reports on the class Actinobacteria (and not the class "Actinobacteria") and the assumption is made that the Judicial Commission (roughly "judicial or impartial commission") the International Commission for the systematics of prokaryotes ( International Committee on Systematics of prokaryotes , ICSP) will determine the order Actinomycetales as a type.

Actinobacteria phylum currently (as of 2018) contains five other classes in addition to the class of the same name: Acidimicrobiia, Coriobacteriia, Nitriliruptoria, Rubrobacteria and Thermoleophilia. These are mostly taxa that were previously listed as a subclass.

Phylum "Actinobacteria"

  • Class Actinobacteria

Sequenced Organisms

The genome-sequenced members of Actinobacteria can be brought into an ancestral relationship by examining orthologous genes . The phylogenetic tree shown shows the relationships between the Actinobacteria (status 2010).

Phylogram (phylogenetic tree) with all sequenced actinobacteria

Selection of some representatives

The family Acidimicrobiaceae in the order Acidimicrobiales in the class Acidimicrobiia contains the genus Acidimicrobium , of which only the species Acidimicrobium ferrooxidans is known. These are rod-shaped bacteria that tend to grow thermophilically (optimum temperature 45–50 ° C). The GC content in the bacterial DNA is 69 mol percent. According to the generic name, they are acidophilic , so they prefer acidic pH values for growth, the optimum is a pH value of 2.0. From the species name it can be deduced that they are able to oxidize iron ( element symbol Fe, Latin for ferrum ) , in fact they oxidize Fe 2+ ions to Fe 3+ ions using oxygen as an oxidizing agent . A. ferrooxidans was u. a. isolated from the ferrous mineral pyrite . It has been proven that a line of this type is able to break down the extremely stable industrial chemicals PFOA and PFOS .

The class Coriobacteriia contains in the order Coriobacteriales the family Coriobacteriaceae with the type species Coriobacterium and the family Atopobiaceae with the type species Atopobium . The species Coriobacterium glomerans was isolated from the gastrointestinal tract of the common fire bug ( Pyrrhocoris apterus ). The cells have a pear-like shape and are strung together in long chains. They grow under obligatory anaerobic conditions, do not form endospores as persistent forms and are not motile . The GC content in the bacterial DNA is 60 mol percent. Since Coriobacterium glomerans as well as Atopobium species form lactic acid and acetic acid in one fermentation , they were initially wrongly assigned to the genera Streptococcus and Lactococcus . These are also gram-positive, but belong to the Firmicutes department. In the case of Atopobium species, it is also noteworthy that their GC content in the bacterial DNA is only 35-46 mol percent, which shows that the original definition of Actinobacteria as gram-positive bacteria with a high GC content does not always apply.

The family Rubrobacteraceae in the order Rubrobacterales in the class Rubrobacteria contains only one genus called Rubrobacter . The types Rubrobacter radiotolerans (formerly Arthrobacter radiotolerans ) and R. xylanophilus are thermophilic, they grow optimally at temperatures of 48–60 ° C. R. radiotolerans was isolated from a hot spring in Japan that had previously been exposed to gamma rays . Only a radiation dose of 10,000 Gray inactivates the bacterium, while a radiation dose of 5 Gray is sufficient for a human cell.

swell

literature

Individual evidence

  1. ↑ a b c d 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. 558-582.
  2. ↑ a b c d e f Erko Stackebrandt, Peter Schumann: Introduction to the Taxonomy of Actinobacteria (Chapter 1.1.1) . In: M. Dworkin, S. Falkow, E. Rosenberg, K.-H. Schleifer, E. Stackebrandt (Ed.): The Prokaryotes. A Handbook on the Biology of Bacteria, Volume 3: Archaea. Bacteria: Firmicutes, Actinomycetes . 3. Edition. Springer-Verlag, New York 2006, ISBN 978-0-387-25493-7 , pp. 297-321 .
  3. ^ A b JA Servin, CW Herbold, RG Skophammer, JA Lake: Evidence excluding the root of the tree of life from the actinobacteria. In: Molecular biology and evolution. Volume 25, Number 1, January 2008, pp. 1-4, ISSN  1537-1719 . doi: 10.1093 / molbev / msm249 . PMID 18003601 .
  4. ↑ RS Gokhale, P. Saxena, T. Chopra, D. Mohanty: Versatile polyketide enzymatic machinery for the biosynthesis of complex mycobacterial lipids. In: Natural Product Reports . Volume 24, No. 2, April 2007, pp. 267-277, ISSN  0265-0568 . doi : 10.1039 / b616817p . PMID 17389997 . (Review).
  5. ↑ M. Rawat, Y. Av-Gay: Mycothiol-dependent proteins in actinomycetes. In: FEMS Microbiology Reviews. Volume 31, No. 3, April 2007, pp. 278-292, ISSN  0168-6445 . doi : 10.1111 / j.1574-6976.2006.00062.x . PMID 17286835 . (Review).
  6. ^ GL Newton, N. Buchmeier, RC Fahey: Biosynthesis and functions of mycothiol, the unique protective thiol of Actinobacteria. In: Microbiology and Molecular Biology Reviews: MMBR. Volume 72, Number 3, September 2008, pp. 471-494, ISSN  1098-5557 . doi: 10.1128 / MMBR.00008-08 . PMID 18772286 . PMC 2546866 (free full text). (Review).
  7. ^ E. Stackebrandt, FA Rainey, NL Ward-Rainey: Proposal for a New Hierarchic Classification System, Actinobacteria classis nov. In: International Journal of Systematic Bacteriology. Volume 47, No. 2, April 1997, pp. 479-491, ISSN  0020-7713 . doi : 10.1099 / 00207713-47-2-479 .
  8. ↑ a b Xiao-Yang Zhi, Wen-Jun Li, Erko 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 Bacteriology . Volume 59, March 2009, pp. 589-608, ISSN  1466-5026 . doi : 10.1099 / ijs.0.65780-0 , PMID 19244447 .
  9. ↑ a b c Wolfgang Ludwig, Jean Euzéby, Peter Schumann, Hans-Jürgen Busse, Martha E. Trujillo, Peter K Merger , William B. Whitman: Road map of the phylum Actinobacteria . In: Bergey's Manual of Systematic Bacteriology . 2nd Edition. Volume 5: The Actinobacteria. 2 volumes. Springer-Verlag, New York 2012, ISBN 978-0-387-95043-3 , pp. 1-28 .
  10. ^ A b Jean Euzéby, Aidan C. Parte: Class Actinobacteria. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved April 3, 2018 .
  11. ↑ a b c d Jean Euzéby, Aidan C. Parte: Phylum "Actinobacteria". In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved April 3, 2018 .
  12. ^ Tree of Actinobacteria. (No longer available online.) In: Eidgenössische Technische Hochschule Zürich (ETHZ) . Archived from the original on August 30, 2011 ; Retrieved February 1, 2010 .
  13. ↑ Nadja Podbregar: Microbe as pollutant eater - soil bacteria break down perfluorinated and polyfluorinated hydrocarbons , based on: scinexx from September 19, 2019
  14. ↑ Lars Fischer: Fluorinated compounds: Bacterium destroys "indestructible" pollutants. In: Spektrum.de. Retrieved October 6, 2019 .
  15. ↑ F. Haas, H. König: Coriobacterium glomerans gen. Nov., Sp. nov. from the Intestinal Tract of the Red Soldier Bug. In: International Journal of Systematic Bacteriology. Volume 38, Number 4, October 1988, pp. 382-384, ISSN  0020-7713 . doi : 10.1099 / 00207713-38-4-382 .

Web links

Commons : Actinobacteria  - collection of pictures, videos and audio files
 Wikispecies: Class Actinobacteria  - Species Directory