Comparative growth of the thermal alga Cyanidium caldarium on nitrate and ammonia at different temperatures

Summary The growth of Cyanidium caldarium on nitrate and ammonia as nitrogen sources was studied at different temperatures from 21 to 54°C.Algal growth occurred at temperatures of 24° C or above when ammonia was the nitrogen source, whereas with nitrate, growth occurred at 30° C or above. The optimum and the maximum growth temperatures were 45 and 54° C respectively on both substrates.Arrhenius plots show that the logarithm of the growth rate is not linear with the reciprocal of absolute temperature, but exhibit sharply defined breaks at 30° C on ammonia and at 40° C on nitrate.It is assumed that below 40° C, when Cyanidium grows on nitrate, the utilization of this substrate represents the master reaction which controls the growth rate of the alga.