Studies on Chlorella regularis, heterotrophic fast-growing strain II. Mixotrophic growth in relation to light intensity and acetate concentration

1) Chlorella regularis showed exponential growth under heterotrophic condition (in the dark with acetate as the carbon source). The growth rate depended on the acetate concentration. Under autotrophic condition (in light with an inorganic medium), growth proceeded exponentially then linearly, in a pattern typical of unicellular algae. The effect of light intensity on the growth rates in the exponential and linear phases was examined. When the cells were cultured under mixotrophic condition (in light with acetate), the growth rate was approximately the same as the sum of the growth rates in the autotrophic and heterotrophic cultures. CMU (50 μm), a specific inhibitor of photosynthesis, caused complete suppression of autotrophic growth, but did not affect heterotrophic growth. When the inhibitor was added to the mixotrophic culture, growth decreased to the level of the heterotrophic culture. These facts indicate that the mixotrophic growth processes of the alga consist of autotrophic and heterotrophic processes that can proceed noncompetitively with each other.