Dynamic Changes of Intestinal Microflora of Chinese Crabs under the Action of Two Typical Environmental Amendments

To evaluate the ecological effects of potassium monopersulfate compound and Bacillus subtilis on the culture of the river crab species, Eriocheir sinensis, four experimental groups were established, including a control group (without environmental amendment), group A (adding both potassium monopersulfate compound), group B (adding B. subtilis), and group AB (adding both potassium monopersulfate compound and B. subtilis). 16S rRNA gene high-throughput sequencing technology was used to analyze the effects of these different environmental amendments on the composition, structure, and function of intestinal microflora of crabs. The results indicate that the contents of total nitrogen (TN), total phosphorus(TP), ammonium nitrogen (NH₄⁺-N), and chemical oxygen demand (COD_Mn) in the water were significantly affected by the processing time of different environmental amendments (P<0.05). TN, TP and COD_Mn showed a trend of first increasing and then decreasing, whereas NH₄⁺-N concentrations were flat at first and then decreased. The concentrations of TN, TP, COD_Mn, and NH₄⁺-N in group AB were significantly lower than those in the control group. Although the application of different environmental amendments did not significantly change the concentrations of TN, TP, COD_Mn, and NH₄⁺-N (P>0.05), but did significantly alter the composition of intestinal microflora. This was mainly reflected in the changes in relative abundances of the phyla Firmicutes, Proteobacteria, and Bacteroidota, as well as differences in the abundance of specific genera such as Citrobacter and Clostridium sensu stricto 1. Community diversity analysis shows that experiment time had a significant effect on microbial diversity (P < 0.05), whereas different environmental amendments did not significantly affect diversity (P>0.05). Community structure analysis identified that the interaction between experiment time and different environmental amendments significantly influenced community composition (P < 0.05), but group AB had a weaker effect in maintaining community stability. Functional prediction analysis indicates that environmental amendments significantly affected the functional potential of the intestinal microflora, particularly in amino acid metabolism, lipid metabolism, secondary metabolite biosynthesis, and signal transduction. The functional differences gradually increased with the extension of experiment time. In conclusion, environmental amendments modulated the composition, structure, and function of the intestinal microflora by improving the culture environment, potentially enhancing the immune and metabolic health of crabs and providing a theoretical basis for optimizing aquaculture environments.