Epulopiscium fishelsoni, or "epulo" for short, is a species of
Gram-positive bacteria that have a symbiotic relationship with
surgeonfish. These bacteria are best known for their large size,
ranging from 200–700 μm in length. Until the discovery of
Thiomargarita namibiensis in 1999, these were the largest bacteria
known. The bacterium has not been grown in the lab, but
scientists have gained a better understanding of it through
1 Naming and discovery
6 Further reading
7 External links
Naming and discovery
Epulopiscium means "banquet of fish" in scientific Latin, from epulum
("feast" or "banquet") and piscium ("of fish"), as the organism was
found inside the gut of fish.
The specific epithet fishelsoni is named for Lev Fishelson, a
Polish-born Israeli ichthyologist who was part of the group that
made the discovery while studying the intestines of a brown
surgeonfish from the
Red Sea in 1985. It was not named until 1988,
by Montgomery (one of the co-discoverers) and Pollak.
They were initially classified as protists on the basis of their large
size, until rRNA analysis by Angert, et al. in 1993 confirmed that
Epulopiscium spp. are bacteria. Their research and studies
illustrated the symbiotic relationship between the host surgeonfish.
Epulopiscium is one of the largest known bacteria, about 1000 times
Escherichia coli or Bacillus subtilis. It is large enough
to be seen with the naked eye at 600 µm. However, because it is
so big, it must compensate for its surface-to-volume ratio, regardless
of its nutrient-rich environment. It also has special coping
mechanisms and structures within it, which were originally thought to
be organelles. These structures form a cortex within Epulopiscium that
are made of vesicles, capsules, and tubules that excrete and transport
waste throughout the cell.
The bacteria exhibit many unusual characteristics, mostly due to the
adaptations necessary for their large size. Epulopiscium spp. are
extremely polyploid, with bacterial chromosomes representing hundreds
of thousands of copies of the genome. Since bacteria rely on
diffusion rather than cytoskeletal transport as in eukaryotes, this
extreme polyploidy allows for the production of gene products at
numerous sites where they are needed in the cell.
Epulopiscium's functions rely heavily on the daily activity of the
brown surgeonfish. During the day, the bacteria is active, restraining
the pH within the surgeonfish's gut. It also reproduces during the
day. During the darker portions of the day, Epulopiscium finishes its
reproduction and becomes inactive and immobile, which causes the pH
level in the surgeonfish's gut to rise. The control that the
bacteria plays over the pH level in the surgeonfish's gut plays a
large role in the fish's digestion because the fish is an
algae-feeding herbivore that also feeds on detritus.
Epulopiscium is unique because it is so large in size, yet it does not
have any organelles or compartments, which has led scientists to
question how it could possibly support itself. Its anatomy helps
it overcome the size limitations inherent in cell volume. The cell's
outer membrane, which is not smooth, contains many folds that increase
the effective surface area. These structures may be involved in
intracellular transport, which would provide a unique example of
convergent evolution on the cellular level.
While these adaptions allow the bacteria to break the theoretical
upper limit for size, the underlying evolutionary reasons for the
bacteria to grow to this size in the first place remain speculative.
One possible reason could be the ability to avoid predation by
Perhaps the most intriguing aspect of the bacterium is its unusual,
almost viviparous reproductive cycle. Its unique reproductive strategy
is the suggested reason why Epulopiscium grows to be such a large
Unlike most bacteria, which undergo binary fission, Epulopiscium
reproduces exclusively through an unusual form of sporulation in which
anywhere from one to twelve daughter cells are grown inside of the
parent cell, until the cell eventually lyses (and dies).
Although sporulation is widespread among other bacteria (such as
Bacillus subtilis) in the phylum Firmicutes, spore formation is
usually brought about by overcrowding, the accumulation of toxins in
the environment or starvation, rather than a standard form of
reproduction. Also, endospores are dormant, while new Epulopiscium
cells are active.
The production of multiple endospores has been observed in other large
gut symbionts such as (Metabacterium polyspora), which are
phylogenetically related to Epulopiscium. Since sporulation affords
bacteria much more protection from the outside environment than binary
fission, it is thought that the evolution of this unusual life cycle
may allow transfer of the bacteria from one host to another.
Different strains of Epulopiscium have been isolated from different
surgeonfish species around the world, and scientists have been unable
to culture Epulopiscium outside of its natural habitat, suggesting
that the relationship between the two is mutually beneficial and
Although the exact biochemical nature of the symbiosis remains
unclear, the bacteria likely assist the fish in breaking down algal
nutrients. Many bacteria of the genus
Clostridium are gut symbionts in
a variety of other species, including humans, often involved in
breaking down complex carbohydrates.
^ a b Montgomery, W. Linn; Pollak, Peggy E. (1988). "Epulopiscium
fishelsoni n. g., n. sp., a Protist of Uncertain Taxonomic Affinities
from the Gut of an Herbivorous Reef Fish". The Journal of
Protozoology. 35: 565–569.
^ Mackie, Roderick; White, Bryan (2012). Gastrointestinal
Microbiology. 1. Springer. p. 172.
^ a b Angert ER, Clements KD, Pace NR (1993). "The largest bacterium".
Nature. 362 (6417): 239–241. doi:10.1038/362239a0.
^ Angert ER, Brooks AE, Pace NR (1996). "Phylogenetic analysis of
Metabacterium polyspora: Clues to the evolutionary origin of
Epulopiscium spp., the largest bacteria". Journal of Bacteriology. 178
(5): 1451–6. PMC 177821 . PMID 8631724.
^ Prescott, Lansing M.; Sherwood, Linda M.; Woolverton, Christopher J.
(2006). "Procaryotic Cell Structureand Function". Microbiology (PDF).
^ Goren, Menachem (2013). "Professor Lev Fishelson, renowned and
respected biologist 1923-2013". Israel Journal of Ecology &
Evolution. 59 (3): 164. doi:10.1080/15659801.2013.899808.
^ "Professor Emeritus, Lev Fishelson". Dept. of Zoology, Faculty of
Life Sciences. Tel Aviv University.
^ Fishelson, Lev; Montgomery, W. Linn; Myrberg, A.A. (1985). "A unique
symbiosis in the gut of tropical herbivorous surgeonfishes
(Acanthuridae: Teleostei) from the Red Sea". Science. 229: 49–51.
^ a b "Epulopiscium fischelsoni". Web.mst.edu. Retrieved
^ Mendell JE, Clements KD, Choat JH, Angert ER (May 2008). "Extreme
polyploidy in a large bacterium". Proc. Natl. Acad. Sci. U.S.A. 105
(18): 6730–6734. doi:10.1073/pnas.0707522105. PMC 2373351 .
^ Ledford H (2008-05-08). "Giant bacterium carries thousands of
genomes". Nature. doi:10.1038/news.2008.806. Retrieved
Epulopiscium fishelsoni - Library". Microbelibrary.org. 2003-05-12.
Archived from the original on 2014-06-06. Retrieved 2014-06-15.
^ Angert ER, Clements KD (2004). "Initiation of intracellular
offspring in Epulopiscium". Molecular Microbiology. 51 (3): 827–835.
doi:10.1046/j.1365-2958.2003.03869.x. PMID 14731282.
^ "Intracellular offspring production by some Firmicutes". The
Epulopiscium Website. Cornell Dept. of Microbiology.
Flint JF, Drzymalski D, Montgomery WL, Southam G, Angert ER (2005).
"Nocturnal production of endospores in natural populations of
Epulopiscium-like surgeonfish symbionts". Journal of Bacteriology. 187
(21): 7460–7470. doi:10.1128/JB.187.21.7460-7470.2005.
PMC 1272977 . PMID 16237029.
Robinow C, Angert ER (1998). "Nucleoids and coated vesicles of
Epulopiscium spp". Archives of Microbiology. 170 (4): 227–235.
doi:10.1007/s002030050637. PMID 9732436.
Epulopiscium spp. and related surgeonfish symbionts, Department of
Microbiology, Cornell University. (Accessed May 2014.)
"Researchers study bacterium big enough to see—the Shaquille O'Neal
of bacteria". Physorg.com. 2008-05-07. Retrieved 2008-05-10.