Photosynthetic Studies With Mutant Strains of Chlorella

Abstract

To obtain mutant strains of Chlorella, cells were suspended in quartz tubes in a complete medium contain-ing 1/5 Moore''s soln., trace elements, glucose, tryptone, yeast extract, and a vitamin mixture. The suspensions were irradiated with u.-v. light of 2,537 A. The irradiation time was varied, and dilution plates of the suspensions were made on a solid complete medium containing the same components as the medium in which the cells were irradiated. The plates were placed under continuous light. Colonies on plates which had 0.1% the number of colonies in nonirradiated controls were used. Transfers were made to agar slants. Inoculations were then made to minimal liquid medium tubes with 1/5 Moore''s soln. and trace elements, growth in the minimal medium being the basis for the detection of biochem. mutants. Absence of growth indicates failure of the cells to synthesize some component of the complete medium. Three strains were unable to grow on the minimal medium. Several others had negligible growth, and 2 of these were also morphological variants. Using the minimal medium plus individual components of the complete medium, that containing glucose only supported growth of the 3 nongrower strains. The mutant strains have remained heterotrophic. Growth of the mutants in light and dark and growth of the wild type in the dark was the same at lower glucose concns. At higher concns. growth of mutants in light exceeded that of mutants and wild type in the dark. Oxygen liberation from photosynthesis was not demonstrated for 2 mutant strains.