The effects of osmotic stress on survival and alkaline phosphatase activity of Aeromonas hydrophila

Abstract

Aeromonas hydrophila was grown under low and high phosphate conditions and inoculated into microcosms containing filtered autoclaved lake water as a starvation medium. Sodium chloride was added to the microcosms to cause osmotic stress and the survival of the bacteria was measured by viable count and ability to respire. The survival of A. hydrophila was dependent upon the concentration of sodium chloride added to the microcosm, with higher concentrations causing a more rapid decline in the viable count. The ability of cells to respire was also gradually lost, but in the microcosms containing 5% and 7% (w/v) sodium chloride, the viable count had fallen below the limits of detection when respiration measurements indicated that 30% of the cells were capable of respiration. Alkaline phosphatase activity increased in the flasks amended with sodium chloride and the osmoprotectant betaine, in both cells with a derepressed alkaline phosphatase and with a repressed alkaline phosphatase. No comparable increase was seen in cells grown with either betaine or sodium chloride alone.