Flow-cytometric study of vital cellular functions in Escherichia coli during solar disinfection (SODIS)

Michael Berney, Hans Ulrich Weilenmann, Thomas Egli

Research output: Contribution to journalArticle

156 Citations (Scopus)

Abstract

The effectiveness of solar disinfection (SODIS), a low-cost household water treatment method for developing countries, was investigated with flow cytometry and viability stains for the enteric bacterium Escherichia coli. A better understanding of the process of injury or death of E. coli during SODIS could be gained by investigating six different cellular functions, namely: efflux pump activity (Syto 9 plus ethidium bromide), membrane potential [bis-(1,3-dibutylbarbituric acid)trimethine oxonol; DiBAC4(3)], membrane integrity (LIVE/DEAD BacLight), glucose uptake activity (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose; 2-NBDG), total ATP concentration (BacTiter-Glo) and culturability (pour-plate method). These variables were measured in E. coli K-12 MG1655 cells that were exposed to either sunlight or artificial UVA light. The inactivation pattern of cellular functions was very similar for both light sources. A UVA light dose (fluence) of <500 kJ m-2 was enough to lower the proton motive force, such that efflux pump activity and ATP synthesis decreased significantly. The loss of membrane potential, glucose uptake activity and culturability of > 80% of the cells was observed at a fluence of ∼ 1500 kJ m-2, and the cytoplasmic membrane of bacterial cells became permeable at a fluence of > 2500 kJ m-2, Culturable counts of stressed bacteria after anaerobic incubation of sodium pyruvate-supplemented tryptic soy agar closely correlated with the loss of membrane potential. The results strongly suggest that cells exposed to > 1500 kJ m-2 solar UVA (corresponding to 530 W m-2 global sunlight intensity for 6 h) were no longer able to repair the damage and recover. Our study confirms the lethal effect of SODIS with cultivation-independent methods and gives a detailed picture of the 'agony' of E. coli when it is stressed with sunlight.

Original languageEnglish (US)
Pages (from-to)1719-1729
Number of pages11
JournalMicrobiology
Volume152
Issue number6
DOIs
StatePublished - Jun 2006
Externally publishedYes

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Disinfection
Sunlight
Escherichia coli
Light
Membrane Potentials
Ethidium
Anaerobic Bacteria
Water Purification
Enterobacteriaceae
Pyruvic Acid
Developing Countries
Agar
Flow Cytometry
Coloring Agents
Adenosine Triphosphate
Sodium
Cell Membrane
Costs and Cost Analysis
Glucose
Acids

ASJC Scopus subject areas

  • Microbiology

Cite this

Flow-cytometric study of vital cellular functions in Escherichia coli during solar disinfection (SODIS). / Berney, Michael; Weilenmann, Hans Ulrich; Egli, Thomas.

In: Microbiology, Vol. 152, No. 6, 06.2006, p. 1719-1729.

Research output: Contribution to journalArticle

Berney, Michael ; Weilenmann, Hans Ulrich ; Egli, Thomas. / Flow-cytometric study of vital cellular functions in Escherichia coli during solar disinfection (SODIS). In: Microbiology. 2006 ; Vol. 152, No. 6. pp. 1719-1729.
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abstract = "The effectiveness of solar disinfection (SODIS), a low-cost household water treatment method for developing countries, was investigated with flow cytometry and viability stains for the enteric bacterium Escherichia coli. A better understanding of the process of injury or death of E. coli during SODIS could be gained by investigating six different cellular functions, namely: efflux pump activity (Syto 9 plus ethidium bromide), membrane potential [bis-(1,3-dibutylbarbituric acid)trimethine oxonol; DiBAC4(3)], membrane integrity (LIVE/DEAD BacLight), glucose uptake activity (2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose; 2-NBDG), total ATP concentration (BacTiter-Glo) and culturability (pour-plate method). These variables were measured in E. coli K-12 MG1655 cells that were exposed to either sunlight or artificial UVA light. The inactivation pattern of cellular functions was very similar for both light sources. A UVA light dose (fluence) of <500 kJ m-2 was enough to lower the proton motive force, such that efflux pump activity and ATP synthesis decreased significantly. The loss of membrane potential, glucose uptake activity and culturability of > 80{\%} of the cells was observed at a fluence of ∼ 1500 kJ m-2, and the cytoplasmic membrane of bacterial cells became permeable at a fluence of > 2500 kJ m-2, Culturable counts of stressed bacteria after anaerobic incubation of sodium pyruvate-supplemented tryptic soy agar closely correlated with the loss of membrane potential. The results strongly suggest that cells exposed to > 1500 kJ m-2 solar UVA (corresponding to 530 W m-2 global sunlight intensity for 6 h) were no longer able to repair the damage and recover. Our study confirms the lethal effect of SODIS with cultivation-independent methods and gives a detailed picture of the 'agony' of E. coli when it is stressed with sunlight.",
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