ABSTRACT
The salt tolerant yeast Candida membranefaciens exhibited a pleiotropic modification in response to high NaCl stress. The in vivo specific activity of Plasma Membrane-ATPase (PM-ATPase) of 1.35 M NaCl adapted cells was enhanced at the mid-log phase. The enhancement in the PM-ATPase activity was NaCl specific as cells stressed with identical concentration of KCl did not have any effect on PM-ATPase. The NaCl specific enhancement in the PM-ATPase activity was associated with decreased Km. Studies on H+ efflux correlated with the results of PM-ATPase. However, in vitro incubation of the enzyme with exogenously added salts like NaCl and KCl invariably inhibited enzyme activity by 70-90% in a dose dependent manner to suggest that in vivo effects of the salts on PM-ATPase were different from the in vitro effects. C. membranefaciens showed a higher intracellular levels of glutamate and aspartate in presence of 1.35 M NaCl which may impart osmoprotection to the stressed cells. It was interesting to observe that the transport activities of aspartate and glutamate were not enhanced according to their relative proportion in the total pool of free amino acids. Instead, transport of these and other amino acids (except lysine and arginine) showed a drastic reduction (upto 90%) in the 1.35 M NaCl grown cells.
Subject(s)
Adenosine Triphosphatases/metabolism , Amino Acids/metabolism , Candida/metabolism , Sodium Chloride/pharmacology , Biological Transport/drug effects , Osmotic PressureABSTRACT
The salt tolerant yeast Candida membranefaciens exhibited a pleiotropic modification in response to high NaCl stress. The in vivo specific activity of Plasma Membrane-ATPase (PM-ATPase) of 1.35 M NaCl adapted cells was enhanced at the mid-log phase. The enhancement in the PM-ATPase activity was NaCl specific as cells stressed with identical concentration of KCl did not have any effect on PM-ATPase. The NaCl specific enhancement in the PM-ATPase activity was associated with decreased Km. Studies on H+ efflux correlated with the results of PM-ATPase. However, in vitro incubation of the enzyme with exogenously added salts like NaCl and KCl invariably inhibited enzyme activity by 70-90% in a dose dependent manner to suggest that in vivo effects of the salts on PM-ATPase were different from the in vitro effects. C. membranefaciens showed a higher intracellular levels of glutamate and aspartate in presence of 1.35 M NaCl which may impart osmoprotection to the stressed cells. It was interesting to observe that the transport activities of aspartate and glutamate were not enhanced according to their relative proportion in the total pool of free amino acids. Instead, transport of these and other amino acids (except lysine and arginine) showed a drastic reduction (upto 90%) in the 1.35 M NaCl grown cells.
Subject(s)
Adenosine Triphosphatases/metabolism , Amino Acids/metabolism , Candida/drug effects , Saline Solution, Hypertonic/pharmacology , Aspartic Acid/metabolism , Biological Transport , Candida/metabolism , Cell Membrane/enzymology , Glutamic Acid/metabolism , Homeostasis/drug effects , Osmotic Pressure , Protons , Saccharomyces cerevisiae/drug effects , Saccharomyces cerevisiae/metabolismABSTRACT
The effect of hypersaline stress on the lipid composition of the salt-tolerant yeast Candida membranefaciens was studied. Fatty acid analyses of the plasma membrane showed a growth phase- and dose-dependent increase in the level of linolenic acid (C18:3) in 1.35 M NaCl-stressed cells. Palmitoleic acid (C16:1) was completely undetectable at all phases of the life cycle. Changes in the levels of other fatty acids were insignificant. The degree of unsaturation of fatty acids in the plasma membranes was higher in presence of 1.35 M NaCl. The fluorescence polarisation value of DPH (1,6-diphenyl- 1,3,5-hexatriene) in the spheroplasts of the stressed cells was lower as compared to the control cells, indicating the fact that a higher membrane fluidity favours osmotic adaptation against NaCl stress. Among different phospholipids, levels of Phosphatidylinositol and Phosphatidylethanolamine were elevated in the salt-adapted cells as compared to their controls. The levels of Phosphatidylcholine and cardiolipin did not change significantly in response to hypersaline stress. The study points out that hypersalinity signals affect the lipid composition which in turn affects the membrane fluidity of C. membranefaciens.
Subject(s)
Candida/metabolism , Membrane Fluidity/physiology , Membrane Lipids/metabolism , Osmotic Pressure , Saline Solution, Hypertonic/pharmacology , Cell Division , Cell Membrane/metabolism , Cell Membrane/ultrastructure , Fatty Acids, Monounsaturated/metabolism , Fluorescence Polarization , Linoleic Acids/metabolism , Membrane Fluidity/drug effects , Phosphatidic Acids/metabolism , Sodium Chloride/pharmacology , Spheroplasts/metabolismABSTRACT
Phosphate uptake studies in different strains of the dimorphic pathogenic yeast Candida albicans were undertaken to show that this yeast actively transported phosphate with an apparent Km in the range of 90-170 microM. The uptake was pH dependent and derepressible under phosphate starvation. Vanadate-resistant (van) mutants of C. albicans showed a 20-70% reduction in the rate of phosphate uptake in high phosphate medium and was associated with an increased Km and reduced Vmax. The magnitude of derepression under phosphate starvation was different between van mutants. These results demonstrate that van mutants may have developed resistance by modifying the rate of entry of vanadate.