Effect of pH and NaCl on the plasma membrane fluidity of the marine yeast Debaryomyces hansenii.
Vera Montiel (1), Martina Turk (2), Ana Plemenitas (2), Jose Ramos (1)
(1) Microbiology, University of Cordoba, Campus de Rabanales, Cordoba, Es, E14080, Spain; (2) Institute of Biochemistry, Medical Faculty, University of Ljubljana, Slovenia
Debaryomyces hansenii is a salt tolerant yeast that grows in low water activity environments like salty water. Two characteristics of sea water are the presence of high salt and high pH and D. hansenii can thrive under those conditions. We have followed a biochemical approach to study the membrane fluidity characteristics when D. hansenii was grown at high salt and at different pHs. By using Electro Paramagnetic Resonance, we have observed three different fluidity domains in the plasma membrane of Debaryomyces. We found out that at low pH the fluidity decreased much more than at a normal or high pH indicating that under those conditions cells are highly stressed. On the other hand, high concentration of NaCl had not an important effect in the distribution of the domains. Fluidity is affected by the type and amount of lipids present in the plasma membrane. Next step was the study of the lipids in the membrane of cells grown under different conditions. Results about the sterol/phospholipid ratio, the amount of sterols and the fatty acids will be shown. When our results were compared to those previously obtained in other yeasts and yeast-like organisms, we found that: . The membrane fluidity profile in D. hansenii is similar to the one found in the salt-sensitive organism S. cerevisiae or in the halotolerant organism Aureobasidium pullulans, . The reported profile for the halophylic Hortaea werneckii was significantly different.