Physiological basis for the high salt tolerance of Debaryomyces hansenii

The effects of KCI, NaCl, and LiCl on the growth of Debaryomyces hansenii, usually considered a halotolerant yeast, and Saccharomyces cerevisiae were compared, KCI and NaCl had similar effects on D. hansenii, indicating that NaCl created only osmotic stress, while LiCl had a specific inhibitory effect, although relatively weaker than in S. cerevisiae, In media with low K+, Na+ was able to substitute for K+, restoring the specific growth rate and the final biomass of the culture, The intracellular concentration of Na+ reached values up to 800 mM, suggesting that metabolism is not affected by rather high concentrations of salt, The ability of D. hansenii to extrude Na+ and Li+ was similar to that described for S. cerevisiae, suggesting that this mechanism is not responsible for the increased halotolerance. Also, the kinetic parameters of Rb+ uptake in D. hansenii (V-max, 4.2 nmol mg [dry weight](-1) min(-1); K-m, 7.4 mM) indicate that the transport system was not more efficient than in S. cerevisiae, Sodium (50 mM) activated the transport of Rb+ by increasing the affinity for the substrate in D. hansenii, while the effect was opposite in S. cerevisiae, Lithium inhibited Rb+ uptake in D. hansenii. We propose that the metabolism of D. hansenii is less sensitive to intracellular Na+ than is that of S. cerevisiae, that Na+ substitutes for K+ when K+ is scarce, and that the transport of K+ is favored by the presence of Na+, In low K+ environments, D. hansenii behaved as a halophilic yeast.