Physiology and Ultrastructure of an Oxygen-resistant Chlorella Mutant under Heterotrophic Conditions.

The oxygen-resistant strain of Chlorella sorokiniana (Shihira and Krauss), distinguished by its ability to grow autotrophically under high partial pressures of oxygen, was studied and partially characterized in heterotrophic culture. Ultrastructural analysis of glucose-grown oxygen-resistant strain and wild type cells reveals that osmiophilic deposits (possibly polyphosphate) are present only in wild type, while oxygen-resistant strain apparently contains increased amounts of starch and endoplasmic reticulum. Of major physiological significance are the observations that: (a) oxygen-resistant strain requires 6 to 8 days to completely adapt to dark, heterotrophic conditions, whereas wild type acclimates in 1 day; (b) oxygen-resistant strain is resistant to high oxygen tension only when grown on glucose, but not on acetate; and (c) the respiratory rate, but not the photosynthetic rate, of heterotrophic oxygen-resistant strain is abnormal compared to wild type.