Shaping the Aquatic Microbiome: Bacillus Probiotics Drive Community Succession and Enhance Nitrogen Cycling in Litopenaeus vannamei Culture Water

This study elucidates the ecological and functional impacts of Bacillus-based probiotics on microbial community dynamics and water quality in Litopenaeus vannamei culture systems. A controlled seven-day experimental framework was employed to compare probiotic-amended and untreated tanks through integrated water quality assessment and high-throughput 16S rRNA gene sequencing. In probiotic-treated water, ammonium concentrations exhibited a consistent decline concomitant with nitrate accumulation, reflecting the enhancement of nitrification and overall nitrogen biogeochemical cycling. Microbial community analyses revealed marked compositional restructuring, characterized by the temporal proliferation of copiotrophic and fast-growing heterotrophic taxa, including Vibrio, Pseudoalteromonas, and Alteromonas. While Bacillus supplementation effectively reduced the relative abundance of potentially pathogenic Vibrio and favored the enrichment of functionally beneficial genera such as Halomonas and Acinetobacter, it also promoted opportunistic successional trajectories within the microbial assemblage. Overall, the results indicate that single-strain Bacillus probiotics can improve water quality through stimulation of nitrogen transformation processes, but may simultaneously trigger unpredictable community-level restructuring, emphasizing the need to consider whole-community responses and to develop multi-strain probiotic formulations for achieving more stable and resilient shrimp aquaculture ecosystems.