Streptomycetaceae

Streptomyces, light microscopy

Streptomycetaceae is a family of bacterial order Actinomycetales. It comprises three genera (as of 2013), the very species-rich genus Streptomyces and fewer species containing genera Kitasatospora and Streptacidophilus. Characteristic are Aerobie, formation of highly branched mycelium resulting from segmentation spores, positive behavior in the Gram stain, high G C content of deoxyribonucleic acid ( DNA) and principal occurrence in soils.

The family Streptomycetaceae is often referred to as a " Streptomyces " or " Streptomyces ". However, these names are not unique, because with it the genus Streptomyces is called.

Shape, cell structure

Streptomycetes form highly branched mycelia usually. The diameter of the mycelial threads ( hyphae ) is 0.5 to 2.0 microns and they grow at their peak. In the hyphae are numerous copies of the chromosomal deoxyribonucleic acid ( DNA), transverse walls are rare. Rarely decompose the hyphae into smaller sections. With ample supply of nutrients to the mycelium developed only in liquid, gel or solid substrate ( substrate mycelium ). Wherein exhaustion of nutrients, the mycelium grows in the gas space ( aerial mycelium ). The aerial hyphae have a hydrophobic outer layer. At the ends of the hyphae of the aerial mycelium ( segmentation) chains are formed of 3 to many spores by their decomposition. Spores each have 1 chromosomal DNA molecule. In Streptomyces coelicolor and Streptomyces lividans, the chromosomal DNA in a linear and in circular form occurs in other Streptomyces species it is only linear. The linear form of DNA of Streptomyces coelicolor contains 8.667 MBP ( million base pairs), 7825 genes. Streptomycetes are gram positive, active movement is missing.

Metabolism

Streptomycetes are aerobic and almost all are Saprobionten with an oxidative chemoorganotrophic energy metabolism, that is, they gain energy by the oxidation of organic substances. As oxidant they typically use molecular, elemental oxygen ( dioxygen, O2 ), some can also use nitrate ( NO3- ) as an oxidant and reduce it to nitrite (NO2 - ). Streptomyces antibioticus reduced nitrate to molecular, elemental nitrogen (N2) and nitrous oxide ( N2O) and is therefore a denitrifier. Streptomycetes possess catalase. An organic substances are sugar and especially biogenic polymers ( macromolecular ) substances ( complex, difficult to degrade ) oxidative degradation, vary by type: starch, pectin, cellulose, chitin, proteins ( such as keratin and elastin ), lignocellulose, aromatics, hydrocarbons and rubber. The lignocellulose -degrading streptomycetes are therefore one of the few lignin -degrading bacteria. Cellulose -degrading streptomycetes were found in the gut of termites. These water-insoluble biogenic substances are first converted into the external medium by secreted enzymes ( exoenzymes ) into water-soluble, low molecular weight products, which are then added to the cells and further reduced. Industrial interest are the hydrocarbon and aromatics -degrading strains, since they are useful in the microbial treatment of petroleum contaminated soils and petroleum products. For the degradation of organic substances streptomycetes use the Embden - Meyerhof pathway, the pentose phosphate pathway also some. The Entner- Doudoroff pathway has not been found in streptomycetes. An exception of type which usually forms organoheterotrophen streptomycetes Streptomyces thermoautotrophicus: This species is obligately chemolithoautotrophic, these strains oxidize inorganic substances for energy, namely molecular, elemental hydrogen ( dihydrogen, H2) and carbon monoxide ( CO). S. thermoautotrophicus is thermophilic, can be used as further special molecular, elemental nitrogen ( dinitrogen, N2) reduce (by means of molybdenum - dinitrogenase ) and thus as a nitrogen source for the development of endogenous substances use (nitrogen fixation) and has a manganese superoxide dismutase.

Streptomycetes form a variety of secondary products such as dyes ( deposited in the mycelium or secreted into the surrounding medium ), various antibiotics and Geosmine that cause the typical earthy smell.

Occurrence of life

As aerobic chemoorganotrophic come streptomycetes in active form, especially in aerobic, anoxic, biogenic organic matter habitats containing before, typically in soils (mostly 104-107 colony-forming units ), but also in freshwater and marine waters ( in sediments and of dead creatures ). There are few obligate halophilic ( high concentrations of salt -loving) streptomycetes. Compost contains many streptomycetes. In the rhizosphere of plants they are well represented. Also in the digestive tract of lower soil animals (worms, arthropods ) they occur. In unfavorable habitats for streptomycetes are probably still only inactive streptomycetes spores. The spores can survive very long unfavorable environmental conditions and they serve to spread.

The optimum temperature of growth is usually at about 25 - 35 ° C, there are few thermophilic ( heat -loving, growing at about 28 - 55 ° C) and psychrophilic ( cold-loving ) streptomycetes. The pH optimum of growth is usually at 6.5 - 8 Therefore, predominantly inhabited pH neutral to slightly alkaline soils by streptomycetes. In acidic soils ( pH about 3.5 ) there is moderate acidophilic streptomycetes, the genus Streptacidophilus characterized by Acidophilie and occurrence in acidic soils. In alkaline soils ( pH range 8 - 11:5) settle alkaliphilic streptomycetes.

There are some plant pathogenic species and very few animal pathogenic. Streptomyces scabiei causing potato scab.