Ward's World Working with Guides

Page 4 Maintaining Algal Cultures Handling Cultures Because algae are photosynthetic, carbon dioxide and a light source are the requirements for growth. Immediately upon receipt, loosen the jar cover or test tube cap to allow gas exchange, and store in a cool area (15 – 20˚C) with dim light. A window with northern exposure is ideal. Avoid storing the algae in direct light, since it will raise the temperature in the jar or tube, creating a miniature "greenhouse effect", damaging the culture. Avoid storing the culture at temperatures over 30˚C because this temperature will damage the cells, reducing the quality of the culture. Stored in ideal conditions, the culture can retain its high quality for several days. If the culture is not going to be used within four to five days, it should be subcultured (transfered to a fresh source of nutrients). Illumination Generally, cultures should be grown in a 16-hour light period alternating with an 8-hour dark period. Ideally, the cultures should be illuminated by 40-watt cool-white fluorescent tubes on a timer. A 40- watt fluorescent tube at a distance of about 15 cm will provide roughly 500 foot candles of illumina- tion. At a distance of approximately 50 cm, the illumination will fall to approximately 200 foot candles. An inexpensive light meter calibrated in foot candles can provide a simple and accurate way to regu- late the light intensity in your lab. Freshwater algal cultures should be grown under a light intensity of 400 to 500 foot candles. At this light intensity, cultures will reach optimum growth in 7 – 14 days, depending on the species and condi- tion of the initial algal inoculum. After this period, reduce the light to 50 – 100 foot candles. Marine algae grow best in slightly lower intensities than those required by freshwater algae — 200 – 300 foot candles. The light cycle and growth period are the same as those recommended for freshwater cultures. Transfer Periods Algal cultures should be transferred at different intervals, depending on the species. After the initial growth period, transfer the cultures to an area with low illumination, where they can be stored for one to six months before subculturing is required again. Some cultures, such as Volvox and Spirogyra, should not be stored and should remain under full illumination. Make new subcultures from the most recently stored cultures. Flagellates generally require subcultur- ing every one to three months. Filamentous algae and unicellular nonmotile algae should be subcul- tured every three to six months. The Volvocales should be subcultured every 7 – 10 days. Marine algae should be subcultured every 1 – 3 months.

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