Probiotic potential of Isochrysis galbana microbiomes against the fish pathogen Vibrio anguillarum

The aquaculture industry is expanding; yet it is challenged by disease outbreaks, many of which are caused by pathogenic bacteria. Such infections can be controlled by antibiotics, however, this contributes to the development and spread of antimicrobial resistance (AMR) and therefore alternative strategies for disease control must be developed. The purpose of this study was to investigate the antibacterial potential of the microbiome associated with the live-feed microalgae Isochrysis galbana. A GFP-tagged highly virulent strain of Vibrio anguillarum (strain 90–11-286) was incubated with different fractions of the algae microbiome and the fluorescence signal was followed to screen for its inhibition. The microalgal microbiome was able to inhibit V. anguillarum and was dominated by Alteromonadaceae and Rhodobacteraceae. When testing isolated pure bacterial cultures, only Phaeobacter could inhibit the pathogen in monoculture, however, given its low prevalence in the microbiome, it was not likely the cause of pathogen inhibition. Co-cultures of Halomonas and Ruegeria were capable of inhibiting the low virulent V. anguillarum strain NB10, however could not inhibit the high-virulent V. anguillarum strain 90–11-286. This study demonstrates that the native microbiomes of microalgae from aquaculture environments hold anti-pathogen potential and highlights the possible benefits of using mixtures of bacteria rather than pure cultures for pathogen suppression.