Listeria innocua and Lactobacillus delbrueckii subsp. bulgaricus employ different strategies to cope with acid stress

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Responses of Listeria innocua and Lactobacillus delbrueckii subsp. bulgaricus to a rapid change in extracellular pH (pHex) from pHex 6 to a range of concentrations down to pHex 3.0 were examined, using HCl and lactic acid (LA) as acidulants. A new fluorescent probe 5-(and-6)-carboxy-2', 7'-dichlorofluorescein diacetate succinimidyl ester (CDCFDA-SE) was employed that enabled reliable measurements of intracellular pH (pHi) to a minimum pHi of 4.0. Changes in pHi and H+ fluxes from immobilised bacteria were measured using fluorescence ratio imaging microscopy (FRIM) and a non-invasive ion flux measuring technique (MIFE), respectively. L. innocua maintained a relatively constant pHi of 5.5-6.1 at pHex 4 and 5 via H+ extrusion. In contrast, L. delbrueckii subsp. bulgaricus progressively lowered pHi towards pHex over the entire pHex range examined. The type of acidulant used influenced pH regulation with both pHi and H+ -fluxes being more severely affected by LA compared to HCl. Overall, our data demonstrated different adaptive strategies in these two bacteria. While L. innocua expels protons to maintain a constant pHi, L. delbrueckii subsp. bulgaricus allows proton entry after acidic treatment so that pHi follows pHex.
Original languageEnglish
JournalInternational Journal of Food Microbiology
Issue number1
Pages (from-to)1-7
Number of pages7
Publication statusPublished - 2006

    Research areas

  • Former LIFE faculty - Listeria innocua; Lactobacillus delbrueckii subsp. bulgaricus; Acid stress; pH homeostasis; pHi; H+ ion flux; Microelectrode technique

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