Growth of Chlorella vulgaris in the Dark

Abstract

Culture flasks of 250 ml. capacity were filled with 150 ml. of complete Hoagland soln. containing glucose and inoculated with 2000 to 10,000 cells/flask; flasks were continually aerated. Flasks placed in the light were detectably green within 5-6 days; those kept in the dark showed no signs of growth. Hemocytometer counts of Chlorella population showed 39,000 cells/mm.3 in a flask kept in light for 6 weeks, while the population of cells in a flask kept in dark for 10 weeks was too low to count. Cells of cultures kept in the dark for long periods are large, granular, and completely lacking in chlorophyll. If exposed to light after a period in darkness, the cells recover their chlorophyll and the population shows rapid growth. A few cultures maintained in the dark for 12 wks. showed no recovery when returned to light. Addition of either yeast extract, indoleacetic acid, glucosamine, asparagine, thiamin, or ascorbic acid to the medium did not promote growth in the dark.