Physiological basis for the high salt tolerance of Debaryomyces hansenii.
The effects of KCl, NaCl, and LiCl on the growth of Debaryomyces hansenii, usually considered a halotolerant yeast, and Saccharomyces cerevisiae were compared. KCl 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 (Vmax, 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.
Prista
C
C
Departamento de Microbiología, Escuela Técnica Superior de Ingenieros Agrónomos, Córdoba, Spain.
Almagro
A
A
Loureiro-Dias
M C
MC
Ramos
J
J
D002414:Cations, Monovalent / Q000494:pharmacology; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D018021:Lithium Chloride / Q000494:pharmacology; D009997:Osmotic Pressure; D011189:Potassium Chloride / Q000494:pharmacology; D012413:Rubidium / Q000493:pharmacokinetics; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D004718:Saccharomycetales / Q000187:drug effects* / Q000254:growth & development / Q000502:physiology*; D012492:Salts / Q000494:pharmacology*; D012965:Sodium Chloride / Q000494:pharmacology; D013045:Species Specificity
D002414:Cations, Monovalent; D012492:Salts; D012965:Sodium Chloride; D011189:Potassium Chloride; D018021:Lithium Chloride; D012413:Rubidium