Biofilm formation and proteolytic activities of Pseudoalteromonas bacteria that were isolated from fish farm sediments

In order to save natural resources and supply good fishes, it is important to improve fish‐farming techniques. The survival rate of fish fry appears to become higher when powders of foraminifer limestone are submerged at the bottom of fish‐farming fields, where bacterial biofilms often grow. The observations suggest that forming biofilms can benefit to keep health status of breeding fishes. We employed culture‐based methods for the identification and characterization of biofilm‐forming bacteria and assessed the application of their properties for fish farming. Fifteen bacterial strains were isolated from the biofilm samples collected from fish farm sediments. The 16S rRNA gene sequences indicated that these bacteria belonged to the genera, Pseudoalteromonas (seven strains), Vibrio (seven strains) and Halomonas (one strain). It was found that Pseudoalteromonas strains generally formed robust biofilms in a laboratory condition and produced extracellular proteases in a biofilm‐dependent manner. The results suggest that Pseudoalteromonas bacteria, living in the biofilm community, contribute in part to remove excess proteineous matters from the sediment sludge of fish farms.