Mitochondria from the salt-tolerant yeast Debaryomyces hansenii (halophilic organelles?)

The yeast Debaryomyces hansenii is considered a marine organism. Sea water contains 0.6 M Na+ and 10 mM K+; these cations permeate into the cytoplasm of D. hansenii where proteins and organelles have to adapt to high salt concentrations. The effect of high concentrations of monovalent and divalent cations on isolated mitochondria from D. hansenii was explored. As in S. cerevisiae, these mitochondria underwent a phosphate-sensitive permeability transition (PT) which was inhibited by Ca2+ or Mg2+. However, D. hansenii mitochondria require higher phosphate concentrations to inhibit PT. In regard to K+ and Na+, and at variance with mitochondria from all other sources known, these monovalent cations promoted closure of the putative mitochondrial unspecific channel. This was evidenced by the K+/Na+-promoted increase in: respiratory control, transmembrane potential and synthesis of ATP. PT was equally sensitive to either Na+ or K+. In the presence of propyl-gallate PT was still observed while in the presence of cyanide the alternative pathway was not active enough to generate a Delta I due to a low AOX activity. In D. hansenii mitochondria K+ and Na+ optimize oxidative phosphorylation, providing an explanation for the higher growth efficiency in saline environments exhibited by this yeast.