Abstract
Cyanidium caldarium grows at acidic pH but not at neutral pH. The intracellular pH of Cyanidium cells has been reported to be kept constant in the neutral pH region by pumping out the proton leaked into the cells according to steep pH gradient. It is not, however, clarified why Cyanidium cells can not grow at neutral pH. In this study, we found that Cyanidium cells survived even at pH 6 over one month, and large cells involving four endospores significantly increased when the cells were cultured at pH 6. This indicates that the cells cultured at pH 6 grow until formation of endospore but can not divide. Furthermore, we found two extracellular proteins at apparent molecular masses of about 34 kDa and 29 kDa in the culture medium at pH 6 but not at acidic pH. Relationship between these extracellular proteins and cell division will be discussed.
