Streptomycetaceae
| Streptomycetaceae | ||||||||||||
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Streptomyces , by light microscopy |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Streptomycetaceae | ||||||||||||
| Waksman & Henrici 1943, emend. Zhi et al. 2009 |
Streptomycetaceae is a family of bacteria - order Actinomycetales . It comprises three genera (as of 2013), the very species-rich genus Streptomyces and the genera Kitasatospora and Streptacidophilus, which contain fewer species . Characteristic are aerobics , the formation of highly branched mycelium with spores arising from segmentation , positive behavior in the Gram stain , high G + C content of deoxyribonucleic acid (DNA) and mainly found in soils .
The Streptomycetaceae family is often referred to as "Streptomycetes" or "Streptomycetes". However, these names are ambiguous because they also denote the genus Streptomyces .
Shape, cell structure
Streptomycetes usually form highly branched mycelia . The diameter of the mycelial threads ( hyphae ) is 0.5 to 2.0 µm and they grow at their tip. The hyphae contain numerous copies of chromosomal deoxyribonucleic acid (DNA), and transverse walls are rare. The hyphae rarely disintegrate into smaller sections. If there is an abundant supply of nutrients, the mycelium only develops in the liquid, gel-like or solid substrate (substrate mycelium). When nutrients are exhausted, the mycelium also grows into the gas space (aerial mycelium). The aerial hyphae have a hydrophobic outer layer. At the ends of the hyphae of the aerial mycelium, chains of 3 to many spores are formed through their dissection (segmentation) . The spores each have 1 chromosomal DNA molecule. In Streptomyces coelicolor and Streptomyces lividans the chromosomal DNA is in linear and circular form, in other Streptomyces species it is only linear. The linear form of Streptomyces coelicolor DNA contains 8.667 MBp (million base pairs ), 7825 genes . Streptomycetes are gram-positive and lack active movement.
metabolism
Streptomycetes are aerobic and almost all are saprobionts with an oxidative chemoorganotrophic energy metabolism , that is, they gain energy through the oxidation of organic substances. As an oxidant , they usually use molecular , elementary oxygen (dioxygen, O 2 ), some can also use nitrate (NO 3 - ) as an oxidant and reduce it to nitrite (NO 2 - ). Streptomyces antibioticus reduces nitrate to molecular, elemental nitrogen (N 2 ) and nitrous oxide (N 2 O) and is therefore a denitrifier . Streptomycetes have catalase . In organic substances, sugars and, above all, biogenic polymer (macromolecular) substances (also complex, difficult to break down) are oxidatively broken down, depending on the type: starch , pectin , cellulose , chitin , proteins (such as keratin and elastin ), lignocellulose , aromatics , hydrocarbons and rubber . The lignocellulose-degrading streptomycetes belong to the few lignin- degrading bacteria. Cellulose-degrading streptomycetes have been found in the intestines of termites . These water-insoluble biogenic substances are first converted into water-soluble, low-molecular-weight products by enzymes excreted in the external medium ( exoenzymes ), which are then absorbed by the cells and further broken down. The strains that break down hydrocarbons and aromatics are of technical interest because they are useful in the microbial cleaning of soils contaminated with petroleum and petroleum products . Streptomycetes use the Embden-Meyerhof route to break down organic matter, and some also use the pentose phosphate route . The Entner-Doudoroff path has not yet been found in streptomycetes. Streptomyces thermoautotrophicus is an exception to the type of usually organoheterotrophic streptomycetes : this species is obligatory chemolithoautotrophic , these strains oxidize inorganic substances to generate energy , namely molecular, elemental hydrogen (dihydrogen, H 2 ) and carbon monoxide (CO). S. thermoautotrophicus is thermophilic , can be used as further characteristic molecular weight elemental nitrogen (dinitrogen, N 2 ) reduce (by molybdenum dinitrogenase ), and thus the body's own as a nitrogen source for the builders use ( nitrogen fixation ), and having a manganese - superoxide dismutase .
Streptomycetes form a variety of secondary products such as dyes (deposited in the mycelium or excreted into the surrounding medium), various antibiotics and geosmins , which cause the typical earth odor.
Occurrence, way of life
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As aerobic chemoorganotrophs, streptomycetes occur in active form primarily in aerobic, oxic habitats containing biogenic organic substances , typically in soils (mostly 10 4 - 10 7 colony-forming units ), but also in limnic and marine waters (in sediments and on dead organisms ). There are only a few obligate halophilic (high salt concentration loving) Streptomycetes. Compost contains a lot of streptomycetes. They are abundantly represented in the rhizosphere of plants . They also occur in the digestive tract of lower soil animals ( worms , arthropods ). In habitats that are unfavorable for streptomycetes, there are probably only inactive streptomycete spores. The spores can survive unfavorable environmental conditions for a very long time and they serve to spread.
The optimum temperature for growth is usually around 25–35 ° C, there are few thermophilic (heat-loving, growth at around 28–55 ° C) and psychrophilic (cold- loving ) streptomycetes. The optimum pH of growth is usually 6.5–8. That is why mainly pH-neutral to slightly alkaline soils are populated by streptomycetes. In acidic soils (pH about 3.5) there are moderately acidophilic streptomycetes, the genus Streptacidophilus is characterized by acidophilicity and occurrence in acidic soils. Alkiphilic streptomycetes live in alkaline soils (pH 8–11.5) .
There are some phytopathogenic species and only a few animal pathogens . Streptomyces scabiei causes potato scab .
literature
- Peter Kämper: The Family Streptomycetaceae, Part I: Taxonomy . Archaea. Bacteria: Firmicutes, Actinomycetes. In: Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (Eds.): The Prokaryotes - A Handbook on the Biology of Bacteria . 3. Edition. tape 3 . Springer, New York 2007, ISBN 978-0-387-25493-7 , pp. 538-604 , doi : 10.1007 / 0-387-30743-5_22 .
- Hildgund Schrempf: The Family Streptomycetaceae, Part II: Molecular Biology . Archaea. Bacteria: Firmicutes, Actinomycetes. In: Martin Dworkin, Stanley Falkow, Eugene Rosenberg, Karl-Heinz Schleifer, Erko Stackebrandt (Eds.): The Prokaryotes - A Handbook on the Biology of Bacteria . 3. Edition. tape 3 . Springer, New York 2006, ISBN 978-0-387-25493-7 , pp. 605-622 , doi : 10.1007 / 0-387-30743-5_23 .
Individual evidence
- ^ Jean Euzéby, Aidan C. Parte: Family Streptomycetaceae. In: List of Prokaryotic names with Standing in Nomenclature ( LPSN ). Retrieved December 23, 2013 .