Abstract
Vibriosis caused by Vibrio anguillarum seriously injures freshwater fish (Salmoniforms) almost every year in Lake Biwa, Japan. This pathogen needs NaCl for its growth and survival. When the pathogen was directly exposed to sterilized aged lake water (ALW) at room temperature, it suddenly lost its culturability and pathogenicity, and died within half a day due to the low osmolarity. In this report, the survival of the pathogen as biofilms formed on air-solid and liquid-solid (agar or polystyrene) interfaces in ALW was investigated. When the biofilms formed at air-solid and liquid-solid (agar or polystyrene) interfaces were exposed to ALW at 4-5°C in the dark, the pathogen survived for more than 2 and 4 weeks, respectively. The biofilms at both interfaces at 4-5°C in the dark enhanced the production of a mucous polymer matrix. The main constituent of the polymer was exopolysaccharide. The polymer was produced only in the dark at low temperature. At 20°C, there was no production of the polymer and the survival of the pathogen was shortened. The biofilm seemed to provide a functional consortium to support the survival of V. anguillarum in freshwater.
