Culturing Euglena

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### **Background**

The various species of the genus Euglena swarm in stagnant pools and ditches, especially those contaminated with fecal matter. The organisms are often so abundant the water becomes green and soup-like in appearance. Euglena have unique anatomy—flagella for mobility, internal chloroplasts for photosynthesis, and a gullet (mouth region) for taking in large food particles. Despite these structures, Euglena thrive better if amino acids are present in the water and the organisms are kept out of direct sunlight. Euglena reproduce asexually. Under stressful conditions, the flagellum is withdrawn, the body becomes spherical, and forms a resistant cyst which can last up to several months. Euglena may be kept in this state for extended periods of time and then revived as needed by adding fresh media. (This property may be useful in a school setting for maintaining cultures during breaks in the school calendar.) Euglena are commonly used by students to evaluate classification criteria and for exploring the difficulties inherent in classifying organisms. Studies of Euglena can illustrate that differences between plants and animals may not be as clear cut as students often believe.

**Culturing/Media**

Upon arrival of Euglena stock cultures, loosen the caps and immediately aerate the cultures by forcing air into the liquid using a clean pipet or an aquarium pump. Cultures should be kept at 16–22 °C and placed in a well-lit area out of direct sunlight. If the cultures get too warm, the heat will drive off oxygen in the water. Artificial illumination from normal fluorescent lights is usually adequate. A certain amount of experimentation may be necessary to find a suitable place to house stock cultures. Initially, it is wise to place multiple subcultures in a variety of sites while trying to determine the best environment for culture storage.

To prepare culture media for Euglena, prepare Chalkley’s Solution.

**Split the culture every ~8 weeks**. Put 1/2 of the culture in another container and set aside (I usually keep the culture until the split culture is well established) then replenish the 1/2 remaining culture with new media.

See Culturing Protists for recomendations.

Shake or stir the media solution and fill shallow containers with wide bottoms approximately half full. (Stacking culture bowls work best.) Add 50–100 mL of Euglena stock culture to each bowl. The Euglena culture medium contains a great deal of organic matter. Bacteria will grow rapidly and the cultures are likely to have a pungent odor for several days. (Take this into consideration when selecting a culture storage location.)

Monitor the vigor of Euglena cultures regularly using a dissecting scope. Cultures can reach a “balance” and thrive for months or can “crash” within several weeks. When a population starts decreasing, transfer culture liquid to fresh media.

**Tips**

• Euglena are small compared to other protists that may be studied by students. Therefore, it is important to have dense, viable cultures to assure student success. Scan for Euglena under low power (40X). Studying Euglena under higher magnification (400X) will reveal the intricate internal structures of Euglena. The green chloroplasts and the long flagellum will be the two most obvious features.

• A solution of methyl cellulose is helpful in slowing down the fast-moving Euglena during microscopic observation.

• Have students view prepared slides of Euglena first.

• Euglena exhibit positive phototaxis.

**Disposal**

Euglena may be disposed of according to Flinn Biological Waste Disposal Method Type IV. Please consult your current Flinn Scientific Catalog/Reference Manual for proper disposal methods.