P and C-NMR Studies of the Phosphorus and Carbon Metabolites in the Halotolerant Alga, Dunaliella salina

The intracellular phosphorus and carbon metabolites in the halotolerant alga Dunaliella salina adapted to different salinities were monitored in living cells by ³¹P- and ¹³C-nuclear magnetic resonance (NMR) spectroscopy. The ¹³C-NMR studies showed that the composition of the visible intracellular carbon metabolites other than glycerol is not significantly affected by the salinity of the growth medium. The T₁ relaxation rates of the ¹³C-glycerol signals in intact cells were enhanced with increasing salinity of the growth medium, in parallel to the expected increase in the intracellular viscosity due to the increase in intracellular glycerol. The ³¹P-NMR studies showed that cells adapted to the various salinities contained inorganic phosphate, phosphomonoesters, high energy phosphate compounds, and long chain polyphosphates. In addition, cells grown in media containing up to 1 molar NaCl contained tripolyphosphates. The tripolyphosphate content was also controlled by the availability of inorganic phosphate during cell growth. Phosphate-depleted D. salina contained no detectable tripolyphosphate signal. Excess phosphate, however, did not result in the appearance of tripolyphosphate in ³¹P-NMR spectra of cells adapted to high (>1.5 molar NaCl) salinites.