Density-dependent sorting of physiologically different cells of Vibrio parahaemolyticus.

A pure bacterial culture is composed of clonal cells in different physiological states. Separation of those subpopulations is critical for further characterization and for understanding various processes in the cultured cells. We used density-dependent cell sorting with Percoll to separate subpopulations from cultures of a marine bacterium, Vibrio parahaemolyticus. Cells from cultures in the exponential and stationary phases were fractionated according to their buoyant density, and their culturability and ability to maintain culturability under low-temperature and low-nutrient stress (stress resistance) were determined. The buoyant density of the major portion of the cells decreased with culture age. The culturability of stationary-phase cells increased with increasing buoyant density, but that of exponential-phase cells did not. Stress resistance decreased with increasing buoyant density regardless of the growth phase. The results indicate that density-dependent cell sorting is useful for separating subpopulations of different culturabilities and stress resistances. We expect that this method will be a powerful tool for analyzing cells in various physiological states, such as the viable but nonculturable state.