Photosynthetic activities of a thermophilic blue-green alga

Abstract

Photosynthetic activities of a thermophilic blue-green alga, a species of Synechococcus, were studied with special reference to its growth at high temperatures. A rapid algal growth occurred in the temperature range between 50 and 60°C, showing the maximum rate, six doublings per day, at about 57°C. Photosynthetic oxygen evolution and methyl viologen photoreduction in the cells were also active at high temperatures and the optimum temperatures for these activities agreed with that of the algal growth. The growth and photosynthetic activities were very low at room temperature and irreversibly inactivated at temperatures above 60°C. The thylakoid membranes isolated from the alga were also photochemically active at high temperatures. The membranes mediated ferricyanide photoreduction coupled with a stoichiometric oxygen evolution at a rate comparable to that of photosynthetic oxygen evolution in the cells. The optimum temperature for the reaction was as high as 50°C. The membranes also showed a photosystem I-mediated reaction at high temperatures. These observations indicate that the thylakoid membranes are intrinsically thermophilic in this organism. Thus the growth of the alga at high temperatures can be well correlated to thermophilic properties of the photosynthetic apparatus.