Studies on marine occurring yeasts: Respiration,fermentation and salt tolerance

Summary The effect of various NaCl concentrations on respiration and fermentation rates in cells with or without added glucose as exogenous substrate as well as on respiratory quotients was determined for Debaryomyces hansenii, Saccharomyces cerevisiae, Cryptococcus albidus, and Candida zeylanoides, all yeasts isolated from marine environment. A given strain had about the same respiratory and fermentatory intensity at 0% and 4% NaCl (w/v). A further increase considerably reduced the oxygen uptake or CO₂-evolution. D. hansenii was the most NaCl tolerant yeast tested, giving about 10% activity still at a concentration of 24% NaCl, whether the activities of whole cells or cell homogenates were determined. For S. cerevisiae or Cr. albidus the respiratory activity was reduced to about the same degree at 16% NaCl for whole cells, at 12% NaCl for homogenates of Cr. albidus. A somewhat higher NaCl concentration was evidently tolerated for respiration and fermentation than for growth, very obvious in the case of C. zeylanoides.The minimum values for water activity (a_w) permitting 10% respiration activity were higher when produced by electrolytes (NaCl, KCl, or Na₂SO₄), lower when due to sugars (metabolizable glucose or non-metabolizable lactose) and lowest when due to glycerol. The a_w per se was evidently not solely decisive for the limitation of respiration activity.Attempts were made to assess an effect of high NaCl concentrations on the glucose uptake.The potassium content was higher in cells of the highly halotolerant D. hansenii than in those of the other yeasts and decreased with the increase in external, consequently in internal, Na⁺ concentration. The decrease in K⁺ content can presumably only proceed to a certain extent, below which the ability for growth and respiration was lost.