AEM Accepts, published online ahead of print on 31 August 2007
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Appl. Environ. Microbiol. doi:10.1128/AEM.01212-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cellular damage in Escherichia coli exposed to combined treatment with high hydrostatic pressure and subzero temperature

Marwen Moussa, Jean-Marie Perrier-Cornet*, and Patrick Gervais

Laboratoire de Génie des Procédés Microbiologiques et Alimentaires, ENSBANA, Université de Bourgogne, 1, Esplanade Erasme, 21000 Dijon, France

* To whom correspondence should be addressed. Email: jperrier{at}u-bourgogne.fr.


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Abstract

The relationship between membrane permeability, changes in cell ultrastructure and cell inactivation was studied in Escherichia coli strain K12TG1 subjected to high hydrostatic pressure treatment at room and subzero temperatures. Propidium iodide staining performed before and after pressure treatment made it possible to distinguish reversible and irreversible pressure-mediated cell-membrane permeabilization. Changes in cell ultrastructure were studied using transmission electron microscopy (TEM), which showed noticeable condensation of nucleoids and aggregation of cytosolic proteins in cells fixed after decompression. A novel technique used to mix fixation reagents with the cell suspension in situ under HHP and subzero temperature conditions made it possible to show partial reversibility of pressure-induced nucleoid condensation. However, based on visual examination of TEM micrographs, protein aggregation did not seem to be reversible.

Reversible cell-membrane permeabilization was noticeable, particularly for HHP treatments at subzero temperature. A correlation between membrane permeabilization and cell inactivation was established, suggesting different mechanisms at room and subzero temperatures. We propose that inactivation of E. coli cells under combined HHP and subzero temperature occurs mainly during their transiently permeabilized state, whereas HHP inactivation at room temperature is related to a balance of transient and permanent permeabilization. Correlation between TEM results and cell inactivation was not absolute. Further work is required to elucidate the effects of pressure-induced damage on nucleoids and proteins during cell inactivation.






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