Intracellular pH homeostasis plays a role in the tolerance of Debaryomyces hansenii and Candida zeylanoides to acidified nitrite.
The effects of acidified-nitrite stress on the growth initiation and intracellular pH (pH(i)) of individual cells of Debaryomyces hansenii and Candida zeylanoides were investigated. Our results show that 200 microg/ml of nitrite caused pronounced growth inhibition and intracellular acidification of D. hansenii at an external pH (pH(ex)) value of 4.5 but did not at pH(ex) 5.5. These results indicate that nitrous acid as such plays an important role in the antifungal effect of acidified nitrite. Furthermore, both yeast species experienced severe growth inhibition and a pH(i) decrease at pH(ex) 4.5, suggesting that at least some of the antifungal effects of acidified nitrite may be due to intracellular acidification. For C. zeylanoides, this phenomenon could be explained in part by the uncoupling effect of energy generation from growth. Debaryomyces hansenii was more tolerant to acidified nitrite at pH(ex) 5.5 than C. zeylanoides, as determined by the rate of growth initiation. In combination with the fact that D. hansenii was able to maintain pH(i) homeostasis at pH(ex) 5.5 but C. zeylanoides was not, our results suggest that the ability to maintain pH(i) homeostasis plays a role in the acidified-nitrite tolerance of D. hansenii and C. zeylanoides. Possible mechanisms underlying the different abilities of the two yeast species to maintain their pH(i) homeostasis during acidified-nitrite stress, comprising the intracellular buffer capacity and the plasma membrane ATPase activity, were investigated, but none of these mechanisms could explain the difference.
Department of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
Henrik Dam
HD
Mortensen
Tomas
T
Jacobsen
Anette Granly
AG
Koch
Nils
N
Arneborg
D000251:Adenosine Triphosphatases / Q000187:drug effects / Q000378:metabolism; D001203:Ascomycota / Q000187:drug effects / Q000254:growth & development*; D002175:Candida / Q000187:drug effects / Q000254:growth & development*; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002473:Cell Wall / Q000187:drug effects / Q000502:physiology; D004361:Drug Tolerance; D005656:Fungal Proteins / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009573:Nitrites / Q000494:pharmacology*
D005656:Fungal Proteins; D009573:Nitrites; D000251:Adenosine Triphosphatases