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Using the technique of synchronous culture, a method has been devised for obtaining a homogeneous population of "giant" cells of the Emerson strain of Chlorella vulgaris.
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Such "giant" cells result from the failure of cell division in heterotrophic cultures initiated with cells in the early stages of their growth cycle. 3. The "giant" cells recover the ability to divide when returned to autotrophic conditions with the production of numerous, normal-sized autospores.
When the Emerson strain of Chlorella vulgaris is cultured on a glucose medium in the dark, the cells are unable to divide normally (Griffiths, 1961). They continue to increase in volume well beyond the point at which they would normally be expected to divide. The "giant" cells so produced may have volumes more than twenty times greater than the largest cells in an autotrophically-grown culture. However, only a proportion of the cells attain the full "giant" dimensions and, after seven days' growth, a heterotrophic culture contains cells having diameters ranging from about 5 & to more than 25 ~.
It has been suggested (Griffiths, 1965) that the range of cell sizes present at the end of the period of heterotrophic growth may be a reflection of certain differences between the individual cells at the time of transfer to the heterotrophic conditions. This possibility is here investigated using the technique of synchronous culture and a method devised for obtaining a homogeneous population of "giant" cells following culture under heterotrophic conditions.
Materials and Methods
Cultures of Chlorella vulgaris (Cambridge Collection 211/11 n) were grown in a liquid inorganic medium (Griffiths, 1965) in flat, one litre bottles in a water bath maintained at 25 ~ C. The bottles were illuminated from the side by a bank of six 40 watt fluorescent tubes, giving a light intensity of 9 kilolux at the culture surface,