Growth of Dictyosphaerium, Selenastrum, and Scenedesmus (Chlorophyceae) in a dilute algal medium

Cultures were maintained in dilute laboratory media for weeks by frequent transfer of cells. Single strains of Scenedesmus and Dictyosphaerium were cultured in a medium with 28.5 mg/l total inorganic salts, with growth at the rate of 1 + doublings/day. Growth of a Selenastrum was compared in one experiment. Bristol's medium was also used for comparison.Routinely, an actively growing inoculum was used, sufficient to give an initial cell concentration of approximately 2 × 105 cells/ml; this was adequate for colorimeter readings. Diurnal light of 3200 lux intensity was used throughout. Each day, after a determination of growth, the culture was transferred, by dilution to the original cell number. Some cultures have been grown in this way for several weeks, and a uniform daily increment in growth is reported here for 10-day experiments. Using this technique we record similar growth rates in sterile-filtered river water used as a medium. Stock cultures can be held in dilute media for several weeks, by first establishing a healthy population, and then maintaining the culture under minimal conditions, usually light at 160–215 lux.