Effect of Bacillus Complex on Water Quality and Bacterial Community Structure of Carassius aumtus Culture Water

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.