Can pressure-induced cell inactivation be related to cell volume compression? A case study for Saccharomyces cerevisiae

Abstract

In this paper, emphasis has been put on the relationship between volume compression and cell inactivation for the Saccharomyces cerevisiae strain CBS 1171 submitted to high hydrostatic pressure treatments. The influence of cell dehydration on pressure inactivation was first investigated. Inactivation was found to be strongly limited, or even completely prevented for cells with a water content of 60% w/w or below. Moreover, the volume compression undergone by a single yeast cell was assessed as a function of pressure and hydration conditions using a high-pressure setup for pressure–volume–temperature measurements. Direct measurements of volume compression were performed on cell pellets after being equilibrated in air at different relative humidity levels (yeast powders). Yeast cells suspended in water–glycerol were assumed to be composed of two compartments: the cytoplasm and the dry matter. The compression of the cell cytoplasm was assumed to be similar to that obtained for water–glycerol mixtures at the same water content. The compression of the dry matter was measured on yeast powder at aw=0.11.Results showed that the magnitude of cell volume compression increased with pressure level. At a given pressure level, cells in a hydrated state underwent higher volume compression than the dehydrated ones. Cell inactivation and volume compression data were then taken together in order to highlight their parallel behaviors. An attempted correlation showed that a cell volume compression of near 10μm3 would be a critical value for cell inactivation. Accordingly, inactivation occurs only when the cell undergoes a sufficient volume compression, regardless of the pressure level. From the thermodynamic point of view, the pressure-induced volume compression indicates the amount of mechanical energy (work of compression) transferred to the cell system. It was suggested that damages at the cellular level, such as the membrane permeabilization, would occur when cells undergo a sufficient volume compression, i.e. mechanical stress and energy. The involvement of protein denaturation, compression of membrane phospholipids, as well as differential in compression between the cell cytoplasm and the plasma membrane, were discussed as possible events leading to cell permeabilization. Cells with compromised membrane integrity are subjected to uncontrolled mass transfers that could lead to inactivation under pressure.