Sodium and potassium transport in the halophilic yeast Debaryomyces hansenii

Debaryomyces hansenii, a halophile yeast found in shallow sea waters and salty food products grows optimally in 0.6 M of either NaCl or KCl, accumulating high concentrations of Na+ or K+. After growth in NaCl or KCl, a rapid efflux of either accumulated cation was observed if the cells were incubated in the presence of KCl or NaCl, respectively, accompanied by a slower accumulation of the cation present in the incubation medium. However, a similar, rapid efflux was observed if cells were incubated in buffer, in the absence of external cations. This yeast shows a cation uptake activity of both Rb-86(+) and Na-22(+) with saturation kinetics, and much higher affinity for Rb-86(+) than for Na-22(+). The pH dependence of the kinetics constants was similar for both cations, and although K values were higher at pH 8.0, there was also an increase in the V-max values. The accumulation of Na-22(+) was found to be increased in cells grown in the presence of 0.6 M NaCl. Rb-86(+) was also accumulated more in these cells, but to a slightly greater extent. The inhibition kinetics of the uptake of Na-22(+) by K+, and that of Rb-86(+) by Na+ was found to be non-competitive. It can he concluded that Na+ in D. hansenii is not excluded but instead, its metabolic systems must be resistant to high salt concentrations. Copyright (C) 2004 John Wiley Sons, Ltd.