Response to low osmotic stress in a fish pathogen, Vibrio anguillarum

Low osmotic stress responses of the fish pathogen, Vibrio anguillarum, were investigated and characterized with regard to changes in cell density and cation type in natural lake water (aged lake water, ALW) and MilliQ water (MQW). This pathogen showed higher survival (% CFU) in ALW than in MQW at all the examined cell densities (106–109 CFU ml−1). Higher resistance in ALW was partially due to divalent cations such as Ca2+ and Mg2+ present in ALW. It was also observed that addition of the supernatant, which was obtained from the pre-suspension of V. anguillarum cells in ALW, significantly increased the survival of the pathogen in ALW. This indicated that the extracellular substance(s) released from the pathogen also played an effective role(s) for survival in ALW. Thus, divalent cations and cell density assist the pathogen, V. anguillarum, to overcome the low osmotic stress in natural freshwater environments.