High internal pH conveys ammonia resistance in spirulina platensis

Spirulina platensis is an alkalophilic cyanobacterium, often cultivated in mass cultures. Unlike many other photosynthetic microorganisms, it is capable of withstanding and even utilizing ammonia at high environmental pH. It is suggested that high internal pH values limit intracellular accumulation of ammonia, thus preventing uncoupling of photosynthesis. Furthermore, it is suggested that the high average internal pH (7.5) is conferred mainly by the intrathylakoid pH which is approximately 1 pH unit higher than in other cyanobacteria tested.