Common Carp Peptidoglycan Gecognition Protein 2 (CcPGRP2) Alleviates Gut Dysbiosis Induced by Aeromonas Hydrophila

Objectives: Peptidoglycan recognition protein 2 (PGRP2) plays a role in regulating immune defense in fish. Our previous studies found that CcPGRP2 helped maintain the integrity of the intestinal mucosa of carp and could bind and agglutinate bacteria when infected with A. hydrophila. However, its effect on the structure of the microbiota has not yet been clarified. Therefore, it is necessary to explore the effect of CcPGRP2 on the intestinal microbiota structure in fish.

Methods: In the present study, common carp were injected with CcPGRP2 protein intraperitoneally and high-throughput sequencing technology was used to study the difference in intestinal microbiota structure. Firstly, the variations in α- and β-diversity of the intestinal microbiota of common carp in control and treatment groups were tested, and the results indicated that intraperitoneal injection of A. hydrophila significantly reduced the microbial α-diversity (within-samples) and β-diversity (between-samples) in common carp gut samples, but CcPGRP2 protein could alleviate these reduction, no matter in the case of simultaneous injection of CcPGRP2 protein and A. hydrophila or a intermitted injection with first injection of CcPGRP2 and then A. hydrophila after 6 h. Subsequently, the intestinal microbiota structures of common carp on various taxonomic levels were interrogated under the treatments.

Results: The data revealed that the abundance of intestinal pathogen Aeromonas was reduced when CcPGRP2 was injected in the common carp, and the alleviation effect was better when CcPGRP2 was injected with A. hydrophila at the same time, implying the function of CcPGRP2 in inhibiting intestinal dysbiosis. Moreover, the functional prediction demonstrated the possible physiological shifts and the influences of microbes on the environment after the common carp is injected with A. hydrophila and CcPGRP2. Finally, the bacterial interaction patterns results showed that the groups injected with A. hydrophila were diverted away from the control group in terms of clustering relationship, while the injection of CcPGRP2 could reverse the effect of A. hydrophila and keep the microbial structure closer to that of the control group; meanwhile, the effect of simultaneous injection of A. hydrophila and CcPGRP2 was better than that of intermitted injections.

Conclusions: All the results in this study suggest that the CcPGRP2 could alleviate the internal dysbiosis under pathogen infection, which will provide a foundation for disease resistance breeding.