Probiotic yeast engineers a protective biofilm environment to enhance bioremediation and seahorse health in aquaculture

Sustainable animal farming via intensive aquaculture relies on a balanced microbial ecosystem that promotes animal well-being. This research explored the use of the probiotic yeast Saccharomyces boulardii to influence tank biofilm microbiomes for improving the health of lined seahorses, Hippocampus erectus . Following a severe mortality event at week 6 that affected both groups, the control group demonstrated partial recovery to 71.4% survival, whereas the probiotic group achieved a higher survival, with a final rate of 88.9% after a disease challenge. This recovery led to a notable reduction in enteritis occurrences with a significant increase in average body weight and a 3.9-fold increase in activity compared to control conditions. Shotgun metagenomic analysis indicated that the enhancements were significantly supported by a marked reorganization of the tank's biofilm community. Probiotic supplementation significantly reduced microbial diversity and selected for a beneficial consortium enriched in taxa with recognized roles in nutrient cycling, including Rhodobacterales (involved in sulfur cycling and pathogen antagonism) and Pirellulaceae (key in polysaccharide breakdown). This engineered biofilm has greater genetic potential for energy generation, glucose degradation, and inorganic ion transfer. Crucially, virulence factor genes and pathogen-associated sequences were substantially suppressed in probiotic-treated biofilms. Our research shows that S. boulardii acts as a crucial modulator, creating a protective biofilm that boosts bioremediation while decreasing pathogenic threats. This ecological approach to the application of probiotics (targeting the environmental rather than host-associated microbiome) may offer a sustainable means to promote health and resilience within aquaculture systems.