Morphological and physiological changes induced by high hydrostatic pressure in exponential- and stationary-phase cells of Escherichia coli: relationship with cell death.
The relationship between a loss of viability and several morphological and physiological changes was examined with Escherichia coli strain J1 subjected to high-pressure treatment. The pressure resistance of stationary-phase cells was much higher than that of exponential-phase cells, but in both types of cell, aggregation of cytoplasmic proteins and condensation of the nucleoid occurred after treatment at 200 MPa for 8 min. Although gross changes were detected in these cellular structures, they were not related to cell death, at least for stationary-phase cells. In addition to these events, exponential-phase cells showed changes in their cell envelopes that were not seen for stationary-phase cells, namely physical perturbations of the cell envelope structure, a loss of osmotic responsiveness, and a loss of protein and RNA to the extracellular medium. Based on these observations, we propose that exponential-phase cells are inactivated under high pressure by irreversible damage to the cell membrane. In contrast, stationary-phase cells have a cytoplasmic membrane that is robust enough to withstand pressurization up to very intense treatments. The retention of an intact membrane appears to allow the stationary-phase cell to repair gross changes in other cellular structures and to remain viable at pressures that are lethal to exponential-phase cells.
School of Food Biosciences, University of Reading, Whiteknights, Reading RG6 6AP, United Kingdom.
Pilar
P
Mañas
Bernard M
BM
Mackey
D001426:Bacterial Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000502:physiology; D022082:Cellular Structures / Q000502:physiology; D004926:Escherichia coli / Q000166:cytology* / Q000254:growth & development / Q000502:physiology*; D006874:Hydrostatic Pressure; D008858:Microscopy, Phase-Contrast; D012329:RNA, Bacterial / Q000378:metabolism
D001426:Bacterial Proteins; D012329:RNA, Bacterial