Micrococcus
Micrococcus luteus (SEM)
Micrococcus is the name of a class of Gram-positive, non-pathogenic in the normally spherical bacteria from the family Micrococcaceae. His name is " Germanized " as Micrococcus (plural: micrococci ) is written, and the term " micrococci " is also used colloquially for the representatives of the family. End of the 20th century there was a redescription of the genus Micrococcus - with assignment of previous Micrococcus species to other genera. Examinations at the beginning of the 21st century led to a further improvement in the description of the genus.
- 3.1 Outer systematics
- 3.2 Internal systematics
- 4.1 Literature
- 4.2 Notes and references
Features
Appearance
The Latinized term Micrococcus is composed of the two Greek components μικρός Mikrós "small" and κόκκος KOKKOS " core ", " grain " together and refers to the appearance in the light microscope: The cell shape is oval round up, it is cocci, are often the cells as so-called tetrads ago - packages of four related cocci. In the Gram stain they behave Gram- positive, do not have flagella for active movement and do not form Überdauerungsformen as endospores.
Growth and metabolism
Micrococcus is strictly aerobic, ie it requires oxygen to grow, this serves as a differentiator to representatives of the family of Staphylococcaceae, glucose anaerobically use in a fermentation with acid formation. His metabolism is marked as chemoorganotroph and heterotrophic, he uses organic compounds as an energy source and also to build up of cellular materials. It is catalase positive and oxidase -positive. Suitable for cultivation temperatures are in the range of 20-40 ° C, which makes it one of the mesophilic organisms. During the growth and alkaline pH values can be tolerated up to pH 10.0.
Chemotaxonomic features
The murein layer of the cell wall contains L-lysine as the diamino acid diagnostically important amino acid. The peptidoglycan type is either A2 ( an inter- peptide bridge connects two tetrapeptides ) or A4α ( an amino dicarboxylic acid - an amino acid with two carboxyl groups - connects two tetrapeptides ). The major menaquinones are MK -8 and either MK -8 (H2 ) or only MK -8 ( H2). In the present in the bacterial menaquinones are quinones, these have an important function in the respiratory chain, similar to ubiquinone in the respiratory chain in humans. Micrococcus species have a high proportion of branched chain fatty acids into their membrane lipids. It is suspected the fatty acids with the abbreviations anteiso - C15: 0 ( pentadecanoic acid, anteiso ) and iso- C15: 0 ( pentadecanoic acid iso- ), in addition to the methyl group (- CH3), which is the branch, still have the peculiarity that they belong with a total of 15 carbon atoms to the odd-numbered fatty acids.
Micrococcus contains a strikingly high GC content in the bacterial DNA, he is 69-76 mole percent. This proves that he is more closely related neither to the genus Sarcina still with the genus Staphylococcus, with their extremely low GC content in the genome characterized (28-31 mole percent and 30-39 mole percent).
Occurrence
Micrococcus is part of the natural flora of the skin in humans, as it is found as a commensal on the skin of other mammals. He is ubiquitous, almost everywhere, for example, in the air, on dust particles, objects, in the upper soil layer in the sea water and fresh water as well as in activated sludge from a sewage treatment plant.
System
→ See also: Taxonomy of the family Micrococcaceae
Outer systematics
Only in 1955 managed to secure distinction of Micrococcus and Staphylococcus, the latter is, anaerobically metabolize glucose in a position even under acid formation. As a result, were classified at the beginning of the 21st century staphylococci and other species in the newly described family of Staphylococcaceae while they were previously grouped with the genus Micrococcus in the family of Micrococcaceae. The in earlier times morphologically based systematics in microbiology led to the M. luteus was formerly known as Sarcina lutea (due to the microscopic appearance ). However, the genus Sarcina one of the anaerobic Endosporenbildnern low GC content of the genome and is not closely related to the genus Micrococcus.
The systematics of microorganisms was formerly based mainly on the appearance, so there were phenotypically oriented pedigrees. With complete description of the structure of DNA in 1953, molecular biological techniques used since about the 90s of the 20th century ( eg, DNA sequence analysis and PCR ) are increasingly genetic traits examined to the phylogenetic development of micro-organisms ( phylogenetic tree) and order to investigate certain relationships in the scheme. The sequences of the so -called 16S ribosomal RNA (rRNA) are studied in prokaryotes. Then based studies and studies chemotaxonomic characteristics by Stackebrandt et al. showed in 1995 that several hitherto the genus Micrococcus associated species to have little in common with M. luteus or M. lylae, so that the original genus was split into five independent: Micrococcus, Kocuria, Nesterenkonia, Kytococcus and Dermacoccus, where the two genera of the newly described family Dermacoccaceae latter have been assigned.
Inside systematics
Examinations at the beginning of the 21st century by Wieser et al. led to a further improvement in the description of the genus Micrococcus, as well as the species M. luteus and M. lylae. Micrococcus luteus is regarded as typical species for the genus.
In 2000, a new species of bacteria was discovered in Antarctica, which is named after the habitat as Micrococcus antarcticus (synonym M. psychrophilum ). Comparisons of the 16S rRNA sequences as well as the chemotaxonomic characteristics (among presence of certain amino acids in the murein layer, main menaquinones ) suggest that the bacterial strain belongs to the genus. Also, the presence of branched fatty acids in the membrane lipids in significant proportions fits to the genus. In addition to saturated fatty acids with the abbreviations anteiso - C15: 0 and iso- C15: 0, a monounsaturated fatty acid anteiso - C15: 1 available. Studies using DNA -DNA hybridization yield DNA-DNA match scores with M. luteus and M. lylae of less than 35 %, which is considered to be sufficiently large phylogenetic distance, so that it is a separate species. The morphological characteristics fit the genre: It is aerobically growing Gram-positive cocci (0.5 microns in size ) that are present as tetrads or diplococci, the cells do not form endospores and are not motile ( they do not have flagella for active movement). The bacterium has adapted to its cold habitat, the optimum growth temperature is about 16 ° C, growth occurs even at 0 ° C, there is consequently a psychrophilic organism.
2007 again a bacterial species was rediscovered, this time in the activated sludge from the bioreactor of a sewage treatment plant. In the complex, the bioreactor in batch mode is used to clean wastewater containing various nitroaromatics and aniline. The isolated bacterial strain Micrococcus flavus called ( flavus from the Latin meaning "yellow" ), because its colonies are colored yellow. Again, the results show chemotaxonomic and molecular biological studies have shown that it belongs to the genus Micrococcus, but it has enough differences to species known to date. DNA-DNA mismatch values with M. luteus, M. and M. lylae antarcticus be 55 %, 48 % and 36 %. Murein layer of the amino acids lysine, glutamic acid, alanine, glycine and aspartic acid are present, the major menaquinones are MK -8 ( H2) and MK-7 (H2). This type is characterized by the presence of branched fatty acids ( anteiso - C15: 0: 0 and iso- C15) of the membrane lipids, and a high GC content in the DNA of 71 mole percent. Similarly, the morphological characteristics similar to those of the genus: It is aerobically growing Gram-positive cocci ( 0.7-1.0 microns in size ), the cells are not motile ( they do not have flagella for active movement). The aerobic metabolism is heterotrophic, M. flavus can use in this way trehalose, dextrin and glycerin (without acidification ). The optimum growth temperature is about 31 ° C ( it is a mesophilic organism ) which is optimal for the growth pH is pH 6.0-6.2.
Currently (2013 ), nine Micrococcus species from the Leibniz Institute DSMZ - German Collection of Microorganisms listed and Cell Cultures GmbH in the Prokaryotic Nomenclature up-to -date ( " Prokaryotic Nomenclature up to date "). This compilation includes all according to the Bacteriological Code validly published names and takes into account the validation list of the International Journal of Systematic and Evolutionary Microbiology. In other species, the assignment to other genera is proposed. The various Micrococcus species and other genera and species in the family Micrococcaceae are listed under the taxonomy of the family Micrococcaceae. The genus Micrococcus has the potential in the future to remain interesting.