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 de nsity and cation type in natural lake water (aged lake water, ALW) and MilliQ water (MQW). This pathogen showed higher survival (% CFU) in A LW than in MQW at all the examined cell densities (10(6)-10(9) CFU ml( -1)). Higher resistance in ALW was partially due to divalent cations s uch as Ca2+ and Mg2+ present in ALW. It was also observed that additio n 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) r eleased from the pathogen also played an effective role(s) for surviva l in ALW. Thus, divalent cations and cell density assist the pathogen, V. anguillarum, to overcome the low osmotic stress in natural freshwa ter environments.