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Aquaculture Water Quality Improvement by Mixed Bacillus and Its Effects on Microbial Community Structure


 Nutrients nitrogen and phosphorus pollution in aquaculture is one of the greatest challenges threatening the survival of aquatic organisms, which requires efficient and sustainable remediation approach. Microbial remediation, especially the application of probiotics, has recently gained popularity in improving the water quality and maintaining the health condition of aquatic animals. In the present study, two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0+BS) and Bacillus megaterium and Bacillus coagulans (A0+BC)) were applied to aquaculture system of Crucian carp to improve the treatment of nitrogenous and phosphorus compounds. The effects of mixed Bacillus on water quality, and the structure and function of microbial communities in aquaculture water were investigated. Our results showed that the improvement effect of mixed Bacillus A0+BS on water quality was better than that of A0+BC, and the NH4+-N, NO2--N, NO3--N and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of bacterial community and decreased the diversity of fungal community. Microbial community analysis showed that mixed Bacillus A0+BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, e.g., Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). The redundancy analysis showed that NH4+-N, NO2--N, and TP were primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the treatment groups were up-regulated, and all pathways in A0+BS group were richer than those in other groups. These results indicated that mixed Bacillus A0+BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.