Persistence of heterologous Flavobacterium psychrophilum genetic variants in microcosms simulating fish farm and hatchery environments

Flavobacterium psychrophilum, the causative agent of bacterial coldwater disease, causes substantial economic losses in salmonid farms and hatcheries. Some multilocus sequence types (ST) of F. psychrophilum are more likely to be associated with fish farms and hatcheries, but it is unclear if these patterns of association represent genetic lineages that are more adapted to aquaculture environments. Towards elucidating the disease ecology of F. psychrophilum, the culturability of 10 distinct F. psychrophilum STs was evaluated for 13 weeks in three microcosms including sterilized well water, sterilized well water with commercial trout feed, or sterilized well water with raceway detritus. All STs remained culturable in each of the microcosms for at least 8 weeks, with bacterial concentrations often highest in the presence of raceway detritus. In addition, most (e.g., 90%) STs remained culturable for at least 13-weeks. Significant differences in log10 cfus were observed among STs, both within and between microcosms, suggesting potential variability in environmental persistence capacity among specific variants. Collectively, results highlight the ability of F. psychrophilum to not only persist for weeks under nutrient-limited conditions but also thrive in the presence of organic substrates common in fish farms and hatchery-rearing units.