Epulopiscium fishelsoni

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Epulopiscium fishelsoni
Systematics
Department : Firmicutes
Class : Clostridia
Order : Clostridiales
incertae sedis
Genre : Epulopiscium
Type : Epulopiscium fishelsoni
Scientific name of the  genus
Epulopiscium
Montgomery & Pollak 1988
Scientific name of the  species
Epulopiscium fishelsoni
Montgomery & Pollak 1988

Epulopiscium fishelsoni (Epulopiscium: guest at a fish's banquet, fishelsoni after the discoverer) is an unusually large gram-positive bacterium . It lives symbiotic in the intestines of surgeon fish , where it helps break down food that the fish has ingested. The species, discovered in 1985, was considered to bethe largest known bacteriumwith lengths of up to 0.6 millimeters until the discovery of Thiomargarita namibiensis in 1999. However, there are also cells that are only 30 µm in size, so that there is a 2000-fold volume difference between large and small members of the species.

In the meantime, some similar cells have also been discovered in other surgeonfish. The species boundaries are not clear at the current state of research. Therefore, Epulopiscium spp. or spoken morphotypes .

physiology

Epulopiscium fishelsoni has a unique anatomy, the specifics of which are mostly used to overcome classical limitations of the size of a bacterium. The reasons for the enormous size are unknown. One possible cause is protection against bacteria-eating protists .

The cell wall is folded in many ways to maximize the surface area. It has a cortex with tubules, vesicles, and other structures that are normally only found in eukaryotes . These structures may be used for intracellular transport. This would make Epulopiscium fishelsoni an unusual example of convergent evolution in the dimensions of single cells.

Epulopiscium fishelsoni type B lives in the intestinal tract of the nasal doctor fish Naso tonganus and becomes 200–300 µm long and 50–60 µm wide. This type has been reported to be highly polyploid and carry up to 200,000 copies of its genome , depending on cell size. The result was a ratio of one copy of the genome to 1.9 μm 3 cytoplasm . Compared to Bacillus subtilis , a normal-sized bacterium with a genome on 0.7 µm 3 cytoplasm, the genome-cytoplasm ratio is therefore of a similar order of magnitude. Epulopiscium fishelsoni type B DNA was found near the cell surface. The authors of the study speculate that this enables a faster response to external, local stimuli than if the genomes were in the middle of the cell. In the giant bacterium Thiomargarita namibiensis , too, the DNA is found on the edge of the cell. Here, however, the metabolically active cytoplasm is limited to a narrow edge by a large central vacuole, which takes up 98% of the cell volume, while in Epulopiscium fishelsoni the central cytoplasm is apparently active.

Due to the cell size and the high number of copies of the genetic material, Epulopiscium has acquired some of the advantages of eukaryotic cells.

Multiplication

One of the most unusual aspects of Epulopiscium fishelsoni is its reproductive behavior. Unlike most bacteria, which reproduce asexually through cell division , Epulopiscium reproduces in a way that presumably originated from sporulation : usually two, but in a morphotype , up to twelve daughter cells grow in the mother cell until it dissolves and release the new individuals.

Multiplication cycle of Epulopiscium fishelsoni 1. Primordia formation : creation of two daughter cells (1.2) in the parent cell (1.1), 2., 3. Growth of the daughter cells, 4. Escape of the daughter cells to the outside

Although sporulation is not uncommon among bacteria (see Bacillus subtilis ), it is usually more of a means in stressful situations than the usual way of reproduction. The daughter cells are also usually dormant, whereas the released cells of Epulopiscium are already active. Other symbiotic intestinal bacteria such as B. Metabacterium polyspora , which are phylogenetically related to Epulopiscium . Possibly, sporulation enables the daughter individuals to be protected from the harsh conditions of the digestive system.

In E. fishelsoni- like endosymbionts, reproduction by division or by mixed forms has also been found.

ecology

Different strains of Epulopiscium have been isolated from the intestines of most surgeonfish species , but a pure culture has not yet been achieved.

The relationship between the surgeonfish and bacteria is classified as mutualism . The exact nature of the relationship is still unknown, but it is believed that Epulopiscium fishelsoni helps fish to obtain nutrients from eaten algae and from detritus .

The daily cycle of Epulopiscium fishelsoni is synchronized with the daily activities of its host. During the day, while the surgeonfish ingests algae, the rounded, compact nucleoids migrate to the ends of the cell and begin to stretch. When they have expanded to around 50 to 75% of the length of the cell in the late afternoon / early evening, sporulation begins.

History and systematics

In 1985, the Israeli scientist Lev Fishelson of Tel Aviv University and colleagues published the discovery of a large, cigar-shaped, initially unnamed protozoan that they found in the intestines of gold spotted surgeonfish ( Acanthurus nigrofuscus ) from the Red Sea . It could reach a size of up to 0.5 mm, around three times the length of a paramecium , but over 85% of the cells were smaller than 0.2 mm. Due to his size, they thought he was a protist , but they could not assign him to any known protist group. Further reasons for classification as a protist were hair-like structures on the cell surface and a structure inside the cell that was mistaken for a cell nucleus . The unicellular organism was found with a density of 20,000 to 100,000 cells per milliliter in the intestine of this herbivorous surgeon fish. The authors considered it to be an organism living symbiotic with the fish. This assumption was supported by the fact that they could find it in each of several hundred specimens of Acanthurus nigrofuscus . It was also discovered in Acanthurus sohal , but not in several other related species.

The name in Epulopiscium fishelsoni was published in 1988.

An rRNA analysis by Pace in 1993 showed that it is a bacterium. Although it could subsequently be assigned to the order of the Clostridiales , its exact systematic position in it is still unclear. The generic name refers to the symbiotic way of life and means something like "guest at the banquet of a fish"; the specific epithet honors the discoverer Lev Fishelson.

In an investigation of the intestinal flora of reef fish in the Pacific , a number of similar protozoa were found in surgeon fish. They have been classified based on their size and their reproductive behavior. Large cells similar to Epulopiscium fishelsoni were found in the gold-spotted surgeonfish A. nigrofuscus and in the blue-stripe surgeonfish Acanthurus lineatus . They are known as the A morphotype. Over ten morphotypes are now known. Since the assignment to species is still unclear, they were referred to as 'Epulos' in their entirety.

Individual evidence

  1. ^ A b Esther R. Angert: Alternatives to binary fission in bacteria. Nature Reviews Microbiology 3, 214-224 (March 2005) doi : 10.1038 / nrmicro1096
  2. ↑ a b c V. Bresler, WL Montgomery L. Fishelson and PE Pollak (1998): Gigantism in a bacterium, Epulopiscium fishelsoni, correlates with complex patterns in arrangement, quantity and segregation of DNA . In: J Bacteriol. 180 (21); 5601-11; PMID 9791108 ; PDF (free full text access)
  3. ^ A b c Web site of Esther Angert at Cornell University , here
  4. ↑ a b c Mendell, JE. et al. (2008): Extreme polyploidy in a large bacterium . In: Proc Natl Acad Sci USA 105 (18); 6730-4. PMID 18445653 doi : 10.1073 / pnas.0707522105
  5. ↑ a b Lev Fish Elson, W. Linn Montgomery and Arthur A. Myrberg, Jr. (1985). A Unique Symbiosis in the Gut of Tropical Herbivorous Surgeonfish (Acanthuridae: Teleostei) from the Red Sea. Science 229 (4708): 49 - 51. doi : 10.1126 / science.229.4708.49
  6. ^ WL Montgomery, PE Pollak (1988): Epulopiscium fishelsoni, NG, N. Sp., A protist of uncertain taxonomic affinities from the gut of an herbivorous reef fish. In: J. Protozool. 35: 565-569. Quoted from Bresler et al. 1998.

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