Euglena gracilis is a freshwater species of euglenid, a microscopic type of , in the genus Euglena. It has secondary , and is a mixotroph able to feed by photosynthesis or phagocytosis. It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 μm long to a sphere of approximately 20 μm. Each cell has two flagella, only one of which emerges from the flagellar pocket (reservoir) in the anterior of the cell, and can move by swimming, or by so-called metaboly across surfaces. E. gracilis has been used extensively in the laboratory as a model organism, particularly for studying cell biology and biochemistry.
Other areas of their use include studies of photosynthesis, photoreception, and the relationship of molecular structure to the biological function of subcellular particles, among others. Euglena gracilis is the most studied member of the Euglenaceae.
E. gracilis was discovered as an effective bioindicator for phenol pollution in freshwater ecosystems and drainage. Their brief generating duration and particular biological reactions make it optimal for measuring phenol concentrations in the natural environment. The reported morphological abnormalities and unusual cell division reveal important information about the biological impacts of phenol on marine organisms. Using E. gracilis as a bioindicator can determine the level of phenol exposure in marine ecosystems and adopt appropriate mitigation actions to protect water quality and biodiversity.
The transcriptome of E. gracilis was sequenced, showing that E. gracilis has many unclassified genes which can make complex and .
Euglena gracilis has 7 to 10 large chloroplasts which are disc- to lens-shaped; at the center of each chloroplast is a pyrenoid with two starch sheaths surrounding the pyrenoid (i.e. double-sheathed). The cell also has numerous round to ring-shaped paramylon grains. The emergent flagellum is about as long as the cell body, occasionally only half as long. There is a single prominent eyespot (stigma).
The plastids contain three membranes. These membranes are an evolutionary vestige of the secondary endosymbiotic event that occurred between a phagotrophic eukaryovorous euglenid and a Pyramimonas-related green alga. The plastids of Euglena are unusual since most secondary plastids are surrounded by four envelopes. The two inner ones are derived from the inner and outer chloroplast envelopes of the primary plastid of the alga that was taken up during the symbiotic event. The two outermost are derived from the plasma membrane of the alga (third) and the phagosome of the host (fourth).
In industry, Euglena gracilis is genetically engineered to produce a flour used to manufacture various protein-rich, non-animal foods.
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