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Applied and Environmental Microbiology, August 2008, p. 4835-4840, Vol. 74, No. 15
0099-2240/08/$08.00+0     doi:10.1128/AEM.00571-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Intracellular pH Homeostasis Plays a Role in the Tolerance of Debaryomyces hansenii and Candida zeylanoides to Acidified Nitrite{triangledown}

Henrik Dam Mortensen,1 Tomas Jacobsen,2 Anette Granly Koch,2 and Nils Arneborg1*

Department of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark,1 Danish Meat Association, Maglegårdsvej 2, 4000 Roskilde, Denmark2

Received 10 March 2008/ Accepted 24 May 2008

The effects of acidified-nitrite stress on the growth initiation and intracellular pH (pHi) of individual cells of Debaryomyces hansenii and Candida zeylanoides were investigated. Our results show that 200 µg/ml of nitrite caused pronounced growth inhibition and intracellular acidification of D. hansenii at an external pH (pHex) value of 4.5 but did not at pHex 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 pHi decrease at pHex 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 pHex 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 pHi homeostasis at pHex 5.5 but C. zeylanoides was not, our results suggest that the ability to maintain pHi 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 pHi 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.

* Corresponding author. Mailing address: Department of Food Science, Faculty of Life Sciences, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark. Phone: 45 35333266. Fax: 45 35333214. E-mail: na{at}life.ku.dk

{triangledown} Published ahead of print on 6 June 2008.

Applied and Environmental Microbiology, August 2008, p. 4835-4840, Vol. 74, No. 15
0099-2240/08/$08.00+0     doi:10.1128/AEM.00571-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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