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''Euglena'' is a genus of single cell
flagellate A flagellate is a cell or organism with one or more whip File:Cat o' nine.JPG, upright=1.35, A leather cat o' nine tails pictured with a U.S dollar bill for size comparison. '' reins, featuring a quirt at the end of the ''romal'' A whip is ...
eukaryote Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...

eukaryote
s. It is the best known and most widely studied member of the class
Euglenoidea Euglenids (euglenoids, or euglenophytes, formally Euglenida/Euglenoida, ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific ...
, a diverse group containing some 54
genera Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying gr ...
and at least 800 species. Species of ''Euglena'' are found in fresh water and salt water. They are often abundant in quiet inland waters where they may bloom in numbers sufficient to color the surface of ponds and ditches green (''E. viridis'') or red ('' E. sanguinea''). The species ''
Euglena gracilis ''Euglena gracilis'' is a freshwater species of single-celled alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthesis, photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes sp ...

Euglena gracilis
'' has been used extensively in the laboratory as a
model organism A model organism (often shortened to model) is a non-human species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is ...
. Most species of ''Euglena'' have photosynthesizing
chloroplast A chloroplast is a type of membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structure ...

chloroplast
s within the body of the cell, which enable them to feed by
autotrophy An autotroph or primary producer is an organism that produces complex organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bo ...
, like plants. However, they can also take nourishment
heterotroph A heterotroph (; from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek ...
ically, like animals. Since ''Euglena'' have features of both animals and plants, early taxonomists, working within the Linnaean two-kingdom system of biological classification, found them difficult to classify. It was the question of where to put such "unclassifiable" creatures that prompted
Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that stud ...

Ernst Haeckel
to add a third living kingdom (a fourth kingdom ''in toto'') to the ''Animale'', ''Vegetabile'' (and ''Lapideum'' meaning ''Mineral'') of
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomi ...

Linnaeus
: the Kingdom
Protista A protist () is any eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...
.


Form and function

When feeding as a heterotroph, ''Euglena'' takes in nutrients by
osmotrophy Osmotrophy is a feeding mechanism involving the movement of dissolved Organic compound, organic compounds by osmosis for nutrition. Organisms that use osmotrophy are called osmotrophs. Some mixotrophic Microorganism, microorganisms use osmotrophy t ...
, and can survive without light on a diet of organic matter, such as
beef extract Meat extract is highly concentrated meat Meat is animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, ...
,
peptone Peptides (from Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ), refers collectively to the dialects of the Greek language spoken ...
,
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetal image:Simple Periodic Table Chart-en.svg, upright=1.75, Nonmetals (and metalloids) in the periodic table: Metalloids are i ...

acetate
,
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
or
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s. When there is sufficient sunlight for it to feed by
phototrophy Terrestrial and aquatic phototrophs: plants grow on a fallen log floating in algae-rich water Phototrophs (''Ancient Greek language, Gr'': φῶς, φωτός = light, τροϕή = nourishment) are organisms that carry out photon capture to prod ...
, it uses chloroplasts containing the pigments
chlorophyll a } Chlorophyll ''a'' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. Chlorop ...

chlorophyll a
and
chlorophyll b } Chlorophyll ''b'' is a form of chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in the mesosomes of cyanobacteria and in the chloroplast Chloroplasts are organelles that conduct photosynthesi ...

chlorophyll b
to produce sugars by
photosynthesis Photosynthesis is a process used by plants and other organisms to convert Conversion or convert may refer to: Arts, entertainment, and media * Conversion (Doctor Who audio), "Conversion" (''Doctor Who'' audio), an episode of the audio drama ' ...

photosynthesis
. ''Euglena's'' chloroplasts are surrounded by three membranes, while those of plants and the
green algae The green algae (singular: green alga) are a large, informal grouping of algae consisting of the Chlorophyta and Charophyta/Streptophyta, which are now placed in separate Division (botany), divisions, together with the more basal Mesostigmatoph ...

green algae
(among which earlier taxonomists often placed ''Euglena'') have only two membranes. This fact has been taken as morphological evidence that ''Euglena's'' chloroplasts evolved from a
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
green alga. Thus, the similarities between ''Euglena'' and plants would have arisen not because of kinship but because of a secondary
endosymbiosis An endosymbiont or endobiont is any organism that lives within the body or cells of another organism most often, though not always, in a mutualism (biology), mutualistic relationship. (The term endosymbiosis is from the Greek language, Greek: ...

endosymbiosis
. Molecular phylogenetic analysis has lent support to this hypothesis, and it is now generally accepted. ''Euglena'' chloroplasts contain
pyrenoid Pyrenoids are sub-cellular micro-compartments found in chloroplast Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the en ...
s, used in the synthesis of
paramylon Paramylon is a carbohydrate similar to starch. The chloroplasts found in ''Euglena'' contain chlorophyll which aids in the synthesis of carbohydrates to be stored as starch granules and paramylon. Paramylon is made in the pyrenoids of ''Euglena''. ...

paramylon
, a form of starch energy storage enabling ''Euglena'' to survive periods of light deprivation. The presence of pyrenoids is used as an identifying feature of the genus, separating it from other euglenoids, such as '' Lepocinclis'' and ''
Phacus
Phacus
''. ''Euglena'' have two flagella rooted in basal bodies located in a small reservoir at the front of the cell. Typically, one flagellum is very short, and does not protrude from the cell, while the other is long enough to be seen with light microscopy. In some species, such as ''Euglena mutabilis'', both flagella are "non-emergent"--entirely confined to the interior of the cell's reservoir--and consequently cannot be seen in the light microscope. In species that possess a long, emergent flagellum, it may be used to help the organism swim. The surface of the flagellum is coated with about 30,000 extremely fine filaments called
mastigonemes A chrysomonad ( Heterokonta: Chrysophyceae) under Transmission electron microscopy">TEM, with a smooth flagellum (1) and a long flagellum covered with mastigonemes (3) Mastigonemes are lateral "hairs" that attach to protistan flagella A fla ...
. Like other euglenoids, ''Euglena'' possess a red eyespot, an organelle composed of
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
pigment granules. The red spot itself is not thought to be
photosensitivePhotosensitivity is the amount to which an object reacts upon receiving photon The photon (Greek: φῶς, phōs, light) is a type of elementary particle. It is the quantum of the electromagnetic field including electromagnetic radiation such a ...
. Rather, it filters the sunlight that falls on a light-detecting structure at the base of the flagellum (a swelling, known as the paraflagellar body), allowing only certain wavelengths of light to reach it. As the cell rotates with respect to the light source, the eyespot partially blocks the source, permitting the ''Euglena'' to find the light and move toward it (a process known as
phototaxis Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive ligh ...
). ''Euglena'' lacks a
cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane cell membrane vs. Prokaryotes The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to a ...
. Instead, it has a pellicle made up of a protein layer supported by a substructure of
microtubule Microtubules are polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, rep ...

microtubule
s, arranged in strips spiraling around the cell. The action of these pellicle strips sliding over one another, known as metaboly, gives ''Euglena'' its exceptional flexibility and contractility. The mechanism of this euglenoid movement is not understood, but its molecular basis may be similar to that of
amoeboid movement Amoeboid movement is the most common mode of locomotion in eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biolog ...
. In low moisture conditions, or when food is scarce, ''Euglena'' forms a protective wall around itself and lies dormant as a resting cyst until environmental conditions improve.


Reproduction

''Euglena'' reproduce asexually through
binary fission Binary may refer to: Science and technology Mathematics * Binary number In mathematics and digital electronics Digital electronics is a field of electronics The field of electronics is a branch of physics and electrical engineeri ...
, a form of
cell division Cell division is the process by which a parent cell (biology), cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle. In eukaryotes, there are two distinct types of cell division; a vegetative ...

cell division
. Reproduction begins with the
mitosis In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical proce ...

mitosis
of the
cell nucleus In cell biology, the nucleus (pl. ''nuclei''; from Latin or , meaning ''kernel'' or ''seed'') is a biological membrane#Function, membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotes usually have a single n ...

cell nucleus
, followed by the division of the cell itself. ''Euglena'' divide longitudinally, beginning at the front end of the cell, with the duplication of flagellar processes, gullet and stigma. Presently, a cleavage forms in the
anterior Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
, and a V-shaped bifurcation gradually moves toward the posterior, until the two halves are entirely separated. Reports of
sexual conjugation Isogamy is a form of sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organism In biology, an organism (from Ancient Gree ...

sexual conjugation
are rare, and have not been substantiated.


Historical background and early classification

Species of ''Euglena'' were among the first protists to be seen under the microscope. In 1674, in a letter to the Royal Society, the Dutch pioneer of microscopy wrote that he had collected water samples from an inland lake, in which he found "animalcules" that were "green in the middle, and before and behind white." Clifford Dobell regards it as "almost certain" that these were ''Euglena viridis'', whose "peculiar arrangement of chromatophores...gives the flagellate this appearance at low magnification." Twenty-two years later, John Harris published a brief series of "Microscopical Observations" reporting that he had examined "a small Drop of the Green Surface of some Puddle-Water" and found it to be "altogether composed of Animals of several Shapes and Magnitudes." Among them, were "oval creatures whose middle part was of a Grass Green, but each end Clear and Transparent," which "would contract and dilate themselves, tumble over and over many times together, and then shoot away like Fish." In 1786, O.F. Müller gave a more complete description of the organism, which he named ''Cercaria viridis'', noting its distinctive color and changeable body shape. Müller also provided a series of illustrations, accurately depicting the undulating, contractile movements (metaboly) of ''Euglenas body. In 1830,
C. G. Ehrenberg Christian Gottfried Ehrenberg (19 April 1795 – 27 June 1876), German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany, ...

C. G. Ehrenberg
renamed Müller's ''Cercaria'' ''Euglena viridis'', and placed it, in keeping with the short-lived system of classification he invented, among the Polygastrica in the family Astasiaea: multi-stomached creatures with no alimentary canal, variable body shape but no pseudopods or lorica. By making use of the newly invented achromatic microscope, Ehrenberg was able to see ''Euglenas eyespot, which he correctly identified as a "rudimentary eye" (although he reasoned, wrongly, that this meant the creature also had a nervous system). This feature was incorporated into Ehrenberg's name for the new genus, constructed from the Greek roots "eu-" (well, good) and glēnē (eyeball, socket of joint). Ehrenberg did not notice ''Euglena''s flagella, however. The first to publish a record of this feature was Félix Dujardin, who added "filament flagelliforme" to the descriptive criteria of the genus in 1841. Subsequently, the class Flagellata (Cohn, 1853) was created for creatures, like ''Euglena'', possessing one or more flagella. While "Flagellata" has fallen from use as a taxon, the notion of using flagella as a phylogenetic criterion remains vigorous.


Recent phylogeny and classification

In 1881, Georg Klebs made a primary taxonomic distinction between green and colorless flagellate organisms, separating photosynthetic from heterotrophic euglenoids. The latter (largely colorless, shape-changing uniflagellates) were divided among the Astasiaceae and the ceae, while flexible green euglenoids were generally assigned to the genus ''Euglena''. As early as 1935, it was recognized that this was an artificial grouping, however convenient. In 1948, Pringsheim affirmed that the distinction between green and colorless flagellates had no taxonomic justification, although he acknowledged its practical appeal. He proposed something of a compromise, placing colorless,
saprotrophic Mycelial cord made up of a collection of hyphae; an essential part in the process of saprotrophic nutrition, it is used for the intake of organic matter through its cell wall. The network of hyphae is referred to as a mycelium, which is fundamental ...
euglenoids in the genus ''Astasia'', while allowing some colorless euglenoids to share a genus with their photosynthesizing cousins, provided they had structural features that proved common ancestry. Among the green euglenoids themselves, Pringsheim recognized the close kinship of some species of ''Phacus'' and ''Lepocinclis'' with some species of ''Euglena''. The idea of classifying the euglenoids by their manner of nourishment was finally abandoned in the 1950s, when A. Hollande published a major revision of the phylum, grouping organisms by shared structural features, such as the number and type of flagella. If any doubt remained, it was dispelled in 1994, when genetic analysis of the non-photosynthesizing euglenoid ''Astasia longa'' confirmed that this organism retains sequences of DNA inherited from an ancestor that must have had functioning chloroplasts. In 1997, a morphological and molecular study of the Euglenozoa put ''Euglena gracilis'' in close kinship with the species ''Khawkinea quartana'', with ''Peranema trichophorum''
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
to both. Two years later, a molecular analysis showed that ''E. gracilis'' was, in fact, more closely related to ''Astasia longa'' than to certain other species recognized as ''Euglena''. In 2015, Dr Ellis O'Neill and Professor Rob Field have sequenced the transcriptome of ''Euglena gracilis'', which provides information about all of the genes that the organism is actively using. They found that ''Euglena gracilis'' has a whole host of new, unclassified genes which can make new forms of
carbohydrate A carbohydrate () is a biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a ...
s and natural products. The venerable ''Euglena viridis'' was found to be genetically closer to ''Khawkinea quartana'' than to the other species of ''Euglena'' studied. Recognizing the polyphyletic nature of the genus ''Euglena,'' Marin et al. (2003) have revised it to include certain members traditionally placed in ''Astasia'' and ''Khawkinea''.


Human consumption

The taste of powdered euglena is described as dried sardine flakes, and contains minerals, vitamins and docosahexaenoic, an omega-3 acid. The powder is used as ingredient in other foods. Kemin Industries sells a euglena nutraceutical supplement ingredient featuring dried ''Euglena gracilis'' with high levels of
beta glucan is an example of a (1→4)-β-D-glucan composed of glucose Glucose is a simple sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated sugar, or regular su ...
.


Feedstock for biofuel production

The lipid content of ''Euglena'' (mainly wax esters) is seen as a promising feedstock for production of biodiesel and jet fuel. Under the aegis of
Itochu is a Japanese corporation based in Umeda is a major commercial, business, shopping and entertainment district in Kita-ku, Osaka, Kita-ku, Osaka, Japan, and the city's main northern railway terminus (Ōsaka Station, Umeda Station). The dis ...
, a start-up company called Euglena Co., Ltd. has completed a refinery plant in Yokohama in 2018, with a production capacity of 125 kiloliters of bio jet fuel and biodiesel per year.Video explanation lacks technical details but suggests degree of government commitment to solving problems of large-scale cultivation and infrastructure. CEO of Euglena Co. wears euglena-green necktie.


Video gallery


See also

* Elysia chlorotica *
Kleptoplasty Kleptoplasty or kleptoplastidy is a symbiotic phenomenon whereby plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the cells of plants, algae, and some other euka ...


References


External links


The Euglenoid ProjectTree of Life web project: EuglenidaProtist Images: EuglenaImages and taxonomy
* {{Taxonbar, from=Q236001 Euglenozoa genera Articles containing video clips Taxa named by Christian Gottfried Ehrenberg