Abstract
The blue-green alga Nostoc sp. strain Mac was grown heterotrophically in the dark on glucose and fructose. Cell composition was similar under photoautotrophic and heterotrophic growth conditions and the efficiency of cell synthesis, in most cases, was similar to values obtained with other heterotrophic micro-organisms. Differences were seen in growth on the two sugars in response to sugar concentration and nitrogen source, and in the efficiency of cell synthesis in minimal medium, which indicated differences in the metabolism of the two sugars by the alga. Heterotrophic growth was stimulated by casein hydrolysate and dim light. Both effects were additive, indicating at least two different rate-limiting steps in the heterotrophic metabolism of the alga. Casein hydrolysate acted as a bulk nitrogen source for the alga and the response to dim light showed a chlorophyll a-like action spectrum.