Sterol content, fatty acid composition of phospholipids, and permeability of labeled ethylene glycols in relation to salt-tolerance of yeasts

Two yeasts, the salt-tolerant Debaryomyces hansenii and the non-tolerant Saccharomyces cerevisiae were grown in basal media (4 m M NaCl) and also a high salinities that produced a similar salt stress in the two species in terms of growth rate reduction (i.e., 1.4 M NaCl for S. cerevisae and 2.7 M NaCl for D. hansenii ). A study was made of the sterol content, the fatty acid composition of the phospholipids, and the permeation of a series of tritiated ethylene glycols of graded molecular weights. On the basis of cell dry weight the amount of total and free sterols increased in both species when cultured at high salinity. Irrespective of growth medium salinity, the molar ratio of free sterols to phospholipids was higher in D. hansenii than in S. cerevisiae . Increased salinity produced only minor changes in the fatty acid composition of the phospholipids in D. hansenii , whereas in S. cerevisiae there was a marked decrease of linolenic acid with a concomitant increase of linoleic acid.
In both yeasts there was an energy linked component in the uptake of ethylene glycol, which component could be inhibited by sodium azide and N -ethylmaleimide. The passive permeability for ethylene-, diethylene- and triethylene glycol increased for both species at increased salinity. This increase was more pronounced for S. cerevisiae than for D. hansenii . Polyethylene glycol of M , 200 as well as higher polyethylene glycols appeared to be excluded or very slowly admitted by the yeasts.