Micrococcus luteus
Micrococcus luteus ( Scanning electron micrograph )
Micrococcus luteus is a Gram-positive bacterium of the genus Micrococcus. The name of the genus is also called " Germanized " is written as Micrococcus. Its cells are aerobic, they can only reproduce so if oxygen is present. As a so -called " air sampling " he is present in the air, but also part of the normal flora of human skin and is regarded as pathogenic. In culture media it grows as yellow-colored colony. Already Alexander Fleming in 1921 examined the effect of which he discovered lysozyme to the bacterium.
The species includes many tribes. The genome of three strains was completely sequenced in the years 2009, 2010 and 2012 respectively. The systematics of the species, as well as the genus, has been updated several times since the late 1990s. The currently ( 2013) the type Micrococcus luteus associated strains differ greatly in many characteristics. Of significance M. luteus is in food microbiology in the determination of the germ content, as well as an indicator in the review of antibiotics.
- 3.1 Outer systematics
- 3.2 Internal systematics
- 3.3 Etymology
- 5.1 Literature
- 5.2 Notes and references
Features
Appearance
The cell shape of the bacterium is round to oval, is cocci. Your typical appearance in the light microscope image is concluded by a peculiarity in cell division, the cells do not separate after each division completely, but remain with the cell wall hanging together. This results in packets of four contiguous cocci, called tetrads. In addition, packages of two cocci ( diplococci ) occur. A single cell has a diameter of about 0.5-3.5 microns. In the Gram stain to M. luteus behaves gram positive, it is so blue stained by the dyes used. This is caused by thicker in the cell wall murein layer. It does not have flagella for active movement can not form Überdauerungsformen as endospores and the bacterial cell wall is surrounded by a capsule.
In pure culture it forms on solid glucose media containing sulfur- yellow to golden-yellow colonies. If no carbohydrate, but only peptone is included, the colonies are colored pale yellow to cream-colored. This - also noted in his name - pigmentation is due to the presence of yellow colored carotenoids.
Growth and metabolism
Micrococcus luteus is strictly aerobic, so it needs oxygen to grow, this serves as a differentiator to representatives of the family of Staphylococcaceae that metabolize glucose anaerobically in a fermentation with acid formation. The bacterium is catalase - positive and oxidase -positive. Temperatures usually used for the cultivation in the range of 25-37 ° C, the optimum temperature is 28 ° C, thus, the bacterium belongs to the mesophilic organisms. The optimum pH for growth is the neutral value, pH 7.0, whereby alkaline pH values can be tolerated up to pH 10.0. M. luteus is relatively insensitive to drought and high salt concentrations, it is still growing in culture media with 10% sodium chloride (table salt), while with a share of 15 % is no more growth.
Characteristic is his aerobic metabolism, it takes oxidizable substrates on which he oxidized with oxygen - this is done with the help of the respiratory chain - and it uses the energy released. This process is also known in bacteria as breathing. Further, its metabolism is marked as chemoorganotroph and heterotrophic, he uses organic compounds as an energy source as well as for the construction of cellular materials. For example, glucose is broken down as an organic substrate oxidation with oxygen to form carbon dioxide and water:
Carbohydrates, which are metabolized in this way are, among others D-glucose, D-mannose, and sucrose. As a reserve material, the bacterium may glycogen - stored in the cell in order to reduce this when you need it to glucose for energy - a polysaccharide of glucose units.
M. luteus has a number of enzymes that are used in metabolism to degrade certain substrates and their credentials are used for identification in the context of a "colorful series". So he has the enzyme nitrate reductase (NADH ) (EC 1.7.1.1 ) and thus can reduce nitrate ( NO3- ) to nitrite (NO2 - ). The enzyme urease to break down urea is not present in all strains. It also has proteolytic enzymes with which he can break down proteins ( proteins).
The bacterium is very sensitive to lysozyme, an anti-bacterial enzyme that is present in egg white, in tears and nasal mucus. Alexander Fleming in 1921 examined the effect of lysozyme on the bacteria and observed a rapid lysis ( " resolution " ) of the cells in a liquid medium. The reason lies in the structure of the cell wall: the case of gram-positive bacteria such as M. luteus this consists of many Mureinschichten, the networking of the glucose -like blocks is cleaved by lysozyme, thus destroying the cell wall. Already 1 ug / ml ( micrograms per milliliter) lysozyme is effective in M. luteus, whereas the Gram-positive Bacillus megaterium also a concentration of 50 ug / ml for the lysis is needed. Fleming named the examined bacterium Micrococcus lysodeikticus 1929, according to the current classification is the strain Micrococcus luteus DSM 20030 (also known as Micrococcus luteus NCTC 2665 Fleming called ).
The mostly yellow color of its colonies is a typical feature and can be attributed to the presence of Sarcinaxanthin, a yellow dye from the group of xanthophylls, which are among the carotenoids. The dye is similar in structure to the zeaxanthin (yellow dye in maize). The pigmentation of " air germs ", ie microorganisms that are found in the air, can be observed frequently. The dyes serve as protection against the UV rays and the rays of visible light. The pigmented bacteria at sites that are exposed to light strongly, an advantage over colorless bacteria that are killed quickly. The pigments in the cell membrane to protect against photo-oxidation in which, for example, cytochromes, major proteins in the respiratory chain, can be destroyed.
This antioxidant effect of Sarcinaxanthin and derived compounds was confirmed by a study from the year 2010. Sarcinaxanthin one of the C50 carotenoid, they contain 50 carbon atoms in the molecule. Such compounds are rarely used as natural dyes, in most previously isolated from natural sources, carotenoids are C40 carotenoids. The biosynthesis of C50- carotenoid Sarcinaxanthin done from two molecules of farnesyl diphosphate (C20 ) as a precursor, and includes lycopene (C40 ), Nonaflavuxanthin (C45), and Flavuxanthin ( C50 ) as intermediates.
Genetics
The genome of the strain Micrococcus luteus Fleming NCTC 2665 was completely sequenced in 2009. The bacterial strain used for the study can be attributed to Alexander Fleming in 1929 as Micrococcus lysodeikticus bacterial strain designated. The genome has a size of 2501 kilobase pairs (kb ), which is about half the size of the genome of Escherichia coli. There are 2236 proteins annotated. Micrococcus luteus SK58 - - In 2010, the genome of another strain was sequenced, this strain was isolated from the human skin. The genome size coincides with 2623 kb slightly larger than for the first investigated trunk, there are 2489 proteins annotated. The end of 2012 was followed by the sequencing of the genome of the strain Micrococcus luteus Modasa, this was in the Indian city of Modasa isolated from hydrocarbon- contaminated soil. The variability of M. luteus strains is currently being explored (2013 ) in other genome projects.
The results of the sequencing show a strikingly high GC content ( the proportion of nucleobases guanine and cytosine) in the bacterial DNA, it is about 73 mole percent. This proves that M. luteus is not related with Sarcina species, which are characterized by particularly low GC content in the genome. Due to the similarity in the microscopic appearance of the bacterium was formerly known as Sarcina lutea. Further genetic testing of M. luteus includes, for example, the gene cluster encoding the enzymes for the biosynthesis Sarcinaxanthin. It was these gene clusters transfer " piece by piece " in an E. coli as a host and as enlightened the individual steps of biosynthesis. In addition, also managed the complete gene expression so that the host bacterium Sarcinaxanthin produced.
A plasmid of the bacterium is used as the object. Referred to as pMEC2 plasmid has a genome size of 4.2 kb to - is thus compared to the bacterial chromosome is very small - and gives M. luteus resistance to macrolide antibiotics such as erythromycin, and lincomycin against. The macrolide resistance is an inducible feature of the bacterium: Only if the culture medium, extremely small amounts (about 0.02-0.05 g / ml ) containing erythromycin, which are not yet sufficient for inhibition of bacterial growth, this acts as an inducer and the corresponding gene product is formed, which M. luteus receives the resistance. A plasmid- inducible resistance in the non-pathogenic, but the normal skin flora bacteria belonging raises the question to what extent they are involved in the spread of antibiotic resistance.
Pathogenicity
M. luteus is usually not pathogenic, it is assigned by the Biological Agents in connection with the TRBA 466 Risk Group 1. However, isolated cases have been observed, in which he called forth (eg, by infection with HIV) infections of the skin in patients with weakened immune systems.
Evidence
The bacterium can be good in liquid or on solid media cultivate containing peptone and meat extract. A selective medium is not available, however, a selective enrichment may be accomplished when the medium has a high salt content (7.5% sodium chloride) and incubated aerobically at about 30 ° C. The pigmentation of the colonies is an indication of M. luteus, as well as the microscopic picture typical cell aggregates in the form of four contiguous cells ( tetrads ). From probably grown on the nutrient medium, facultative anaerobic Staphylococci can be distinguished by an oxidation - fermentation test (OF ) test, since they form both aerobic as well as anaerobic acid from glucose, whereas glucose can metabolize micrococci with oxygen. Further biochemical tests to identify include the catalase and oxidase test, and typical tests of a "colorful series ", where among other things the usefulness of various carbohydrates and other substrates is investigated. Here, M. luteus behaves positively in nitrate reduction, negative for indole formation, Voges - Proskauer positive in the reaction and is urease - variable. A work based on the rapid determination system in miniature (Analytical Profile Index ) for the determination of bacteria from the family Staphylococcaceae is commercially available and also includes the detection of Micrococcus species.
Occurrence
Micrococcus luteus is a so-called " air sampling " means ( colloquially it is also called "Yellow Luftkokkus " ), as it often grows on nutrient media in Petri dishes, which are used in an air sampling. He is ubiquitous, almost everywhere, in addition to the room air for example dust particles, objects, and in the upper soil layer. He is also part of the natural flora of the skin in humans. He is mainly traceable to the more unclothed body parts. It was spread to other habitats, such as sea water and fresh water, plants, and meat and dairy products on human beings or the air.
Documented, for example, the isolation of M. luteus strains from soil, activated sludge from a sewage treatment plant, sea water, a piece of coral, the human skin, medieval wall painting, interior air, from cheese and rotten meat.
System
Outer systematics
Micrococcus luteus was described in 1872 by Ferdinand Cohn on work done by Joseph Schröter. Cohn had grown the bacteria on a potato breeding ground. In the same work Cohn had first developed an anabolic Darwin classification scheme for bacteria with genus and species names. Only in 1955 managed to secure distinction of Micrococcus and Staphylococcus species. 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. End of the 20th century there was a redescription of the genus Micrococcus by Stackebrandt et al - 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 Micrococcus, as well as the kinds M. luteus and M. lylae by Wieser et al Micrococcus luteus is the type species of the genus.
Inside systematics
The in earlier times morphologically based systematics in microbiology results in M. luteus is known by many synonyms. These are the already -mentioned terms Micrococcus lysodeikticus (experiments of Fleming with lysozyme ) and Sarcina lutea (due to the microscopic appearance ), but also Sarcina citrea and Sarcina flava. Schröter 1872 had the bacterium originally called Bacteridium luteum.
Studies from the years 1999 to 2002 show an amazing diversity of the species Micrococcus luteus, namely with respect to chemotaxonomic characteristics and biochemical and metabolic physiological properties. To elucidate the evolutionary history - and the family relationships of organisms to each other - we examined the DNA sequences in bacteria and in addition, the 16S rRNA, a typical representative for prokaryotes the ribosomal RNA. Genetic studies of DNA sequences by DNA -DNA hybridization and 16S rRNA analysis of the sequences exhibit at M. luteus indicate a close relationship of the strains studied, so that they remain allocated all the way or be reassigned. The following strains are distinguished (as of 2013):
- Micrococcus luteus NCTC 2665 is the species- typical strain. Synonyms for this are Micrococcus luteus NCIB 9278, Micrococcus luteus CCM 169, Micrococcus luteus ATCC 4698 (equivalent to ATCC 15307 ), Micrococcus luteus DSM 20030, Micrococcus luteus CN 3475, Micrococcus luteus Fleming NCTC 2665th Equivalent designations are Micrococcus luteus strain ( strain) NCTC 2665 and Micrococcus luteus str. NCTC 2665th This is the " Fleming strain", the genome is sequenced ( biovar I).
- Micrococcus luteus SK58. Equivalent designations are Micrococcus luteus strain ( strain) and Micrococcus luteus SK58 st. SK58. It was isolated from the human skin, the genome has been sequenced.
- Micrococcus luteus str. Modasa. He was isolated from contaminated soil in India, the genome is sequenced.
- Micrococcus luteus MU201. He was isolated from cheese, the genome project is in progress.
- Micrococcus luteus CD1_FAA_NB_1. This strain is investigated in the framework of the Human Microbiome Project ( Human Microbiome Project, HMP ). The HMP was initiated in 2008 by the U.S. National Institutes of Health (National Institutes of Health ) and has the aim to characterize the human microbiome closer. The genome project is in progress.
- Micrococcus luteus DSM 14234, synonym Micrococcus luteus CCM 4959th He was isolated from a medieval wall painting in Austria and was during the investigation as strain D7 referred ( biovar II).
- Micrococcus luteus DSM 14235, synonym Micrococcus luteus CCM 4960th He was from activated sludge from a wastewater treatment plant in Ballarat (Australia) and was isolated during the study as a strain called Ballarat ( biovar III).
Assigning three biovars is the result of the above examinations. It was decided not to division into subspecies ( subspecies ), instead there was a more formal separation into biovars. The term " biotype " is based on the biological variability of the studied organisms.
In the case of M. luteus this betriftt v. a chemotaxonomic characteristics were examined existing in the bacterial menaquinones, these quinones have an important function in the respiratory chain, similar to ubiquinone in the respiratory chain in humans. With respect to the construction of the bacterial cell wall, the polar lipids and diamino acids were investigated in order to characterize the type of the peptidoglycan ( murein ). Further investigations include the breakdown of carbohydrates and other substrates. The following table gives an overview of the findings and order of the properties of the three biovars again.
Usually, the bacterial strains show a kind of greater similarities in phenotypic traits. Thus significant variations within a species have not been observed. But It must be borne in mind that an organism -Art is not a static entity, but - as seen for a long time - changed. One possible interpretation of these results is that they show only a "snapshot" in the course of evolution.
Etymology
The genus name can be traced back to the appearance of the cells ( micros from ancient Greek meaning " small", kókkos ancient Greek for " berry " ), the species name refers to the appearance of the colonies ( luteus from the Latin meaning " golden ").
Importance
Produced by M. luteus carotenoid Sarcinaxanthin offers the potential economic use. Carotenoids act as antioxidants ( " free radical scavengers ") that are already marketed for this purpose as food additives or supplements. A use as a food color - similar to beta carotene - is conceivable.
Of importance, the bacterium is already used as an indicator in the review of antibiotics. M. luteus is sensitive not only to lysozyme, but is inhibited by several antibiotics, such as chloramphenicol, erythromycin, neomycin and streptomycin in growth. In a so-called sensitivity testing is to determine whether a micro-organism ( usually a pathogen ) to a particular antibiotic is sensitive or resistant to this is, after the result is intended ideally the antibiotic therapy. Conversely, you can also investigate how microorganisms a particular antibiotic acts by placing a small plate with a defined amount of an antibiotic in the middle of the nutrient medium in a petri dish and various bacterial species crosses out radially thereto ( see figure). If the bacteria is not sensitive to the active substance, it grows right up to the plate, otherwise inhibits the diffused into the culture medium antibiotic its growth. In a review of an antibiotic is introduced M. luteus with as a positive control, if already known beforehand that he is sensitive.
A future ecologically and economically interesting application of certain M. luteus strains lies in their ability to bind as a complexing metal ions. Studies show that this include ores containing gold and strontium at low levels, is possible, so that an accumulation of metals can be carried out using the bacterium. Also a microbiological remediation of contaminated soils is feasible - by the strain M. luteus str. Modasa - which is capable of degrading hydrocarbons and therefore can potentially be used for the removal of petroleum residues in the soil.
From the perspective of food microbiology is M. luteus important. Since it is non-pathogenic, there is no direct limit or guide values. However, its growth on foods lead to spoilage because it feeds on the organic ingredients. The presence of the bacteria thus leads to an accumulation of metabolic products in the food and also to loss of the ingredients. Here are the proteolytic enzymes of M. luteus of importance with which he can break down proteins ( proteins). This results in numerous proteinous food (such as meat products) to spoilage, without causing food poisoning.
To prevent this, hygienic measures in the production and packaging of food are to be applied, continue to limit or guide values for bacterial groups are defined. This is particularly the " mesophilic aerobic colony count ," including all bacteria are summarized from the foods that (20-40 ° C) grow with oxygen at moderate temperatures on a complex nutrient medium, thus form colonies. Since M. luteus is aerobic and mesophilic and also very widespread, it is an important representative of this group dar. values for the mesophilic aerobic colony count shall be published by the German Society for Hygiene and Microbiology, this example be