Chapter 10 Hmdling and Culturing of Chlorella

Abstract

This chapter discusses successful culturing and growing of Chlorella and other unicellular green algae. The organisms comprising the genus Chlorella are nonmotile, globular, unicellular green algae with an average diameter of 4 to 10 μ . Chlorella are dependent on light for autotrophic growth; therefore, the course of the growth curve is governed by the illumination of the culture. For most investigations three species of Chlorella are in use. These are C. vulgaris , C. pyrenoidosa , and C. ellipsoidea . In all of these species different strains are known, which differ markedly in physiological characteristics. Pure cultures are always derived from a single parent cell and are propagated with the precautions necessary to prevent contamination by other microorganisms. Moreover, to retain these cultures over a longer period of time, it is advantageous to prepare test tube cultures using media solidified with 1% agar. In connection with the handling and keeping of stock cultures over a period of years, the problem of constancy with respect to morphological and physiological characteristics is very important. Among most of the frequently used strains of Chlorella there is no evidence of a tendency for much spontaneous mutation. To obtain synchronization in cultures of Chlorella, a change of at least one external factor is required. Although autotrophic microorganisms can generally be grown in continuous light, the light-dark change seems to be the most suitable procedure to synchronize Chlorella.