Modification of thermal response of Chlorella ellipsoidea by deuteration

The isotope effect of deuterium (D) on cellular thermo-response, one of the major cell functions, was pursued by using deuterated Chlorella ellipsoidea which was grown in D2O medium and deuterated proportionally to the concentration of D2O in the medium. The deuterated Chlorella (D-Chlorella) cells heat-treated at 43°C in H2O medium were more heat-sensitive than control Chlorella (H-Chlorella) cultured in H2O medium. The D-Chlorella cells grown in higher mol% D2O were more heat-sensitive than those grown in lower mol% D2O. On the other hand, both the D- and H-Chlorella cells heat-treated at 43°C in D2O medium were more heat-resistant than in H2O medium. The degree of heat resistance was linearly proportional to the concentration of D2O in the medium. These results suggest that D in the medium and cells had two opposite effects on Chlorella; deuteration of poorly exchageable regions of biomolecules in the cells made Chlorella heat-sensitive, and both D2O in the medium and D in easily exchangeable regions caused Chlorella to be heat-resistant.