31P and 13C-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 (31)P- and (13)C-nuclear magnetic resonance (NMR) spectroscopy. The (13)C-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 T(1) relaxation rates of the (13)C-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 (31)P-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 (31)P-NMR spectra of cells adapted to high (>1.5 molar NaCl) salinites.