Abstract: Bacillus megaterium (A0), Bacillus coagulans (BC), Bacillus subtilis (BS) were compared for their degradation effects on aquaculture water. The effects of the combination of A0+BC and A0+BS on N and P concentrations and bacterial community structure in carp culture water were studied. The results show that the degradation effects of A0+BS on NH₄⁺-N, NO₂^--N, NO₃^--N and TP were the most significant, and the degradation rates were 46.3%, 76.3%, 35.6% and 80.3%, respectively. The concentration of TP and NH₄⁺-N conformed to the 3rd grade of National Surface Water Environmental Quality Standard. The concentration of TP in group A0+BC was always higher than that in CK. This result suggests that the combination of A0 and BS had synergistic effect on the removal of NH₄⁺-N, NO₂^--N, NO₃^--N, TP, and previous studies show that Bacillus coagulans had no degradation effect on TP. The microbial communities were profiled by high-throughput sequencing of the V3-V4 hypervariable region of 16S rRNA gene using the MiSeq Illumina sequencing platform. The results show that the microbial community diversity in the A0+BS group was the highest. In addition, adding Bacillus complex in aquaculture water reduced the number of Bacteroidets, increased Proteobacteria and Actinobacteria. The relative abundance of Actinobacteria in the A0+BS group was the highest. Lysinibacillus, Solibacillus and Haematobacter were mainly dominant bacterias in the CK group. The dominant strain was Comamonas belonging to heterotrophic nitrification-aerobic denitrifying bacteria in A0+BC and A0+BS group. Other dominant bacteria in A0+BC group Acinetobacter and Pseudomonas were pathogenic bacteria. In A0+BS group dominant bacteria Bosea and Dokdonella were denitrifying bacteria. A0+BS regulated the microbial community structure in the aquaculture water, which improved the water quality of the aquaculture water.

Key words: Bacillus complex, Carassius aumtus, water quality, high-throughput sequencing, bacterial community structure