Changes in Hemolymph Microbiota of Chinese Mitten Crab (Eriocheir sinensis) in Response to Aeromonas hydrophila or Staphylococcus aureus Infection

SIMPLE SUMMARY: Chinese mitten crab (Eriocheir sinensis), which has nutritional and delicious qualities, is an economically important farmed crab species. Unfortunately, bacterial diseases often occur during the breeding process in Chinese mitten crabs, resulting in significant economic losses. The role of the hemolymph microbiota in modulating physiological and biochemical functions in crustaceans is well established. However, role of the hemolymph microbiota of E. sinensis in relation to infections remains underinvestigated. Here, we studied the changes in the composition and function of the hemolymph microbiota in E. sinensis infected with either Staphylococcus aureus or Aeromonas hydrophila. Diverse patterns of structural alterations were observed in the hemolymph microbiota of crabs when exposed to various pathogens. The dynamic shifts in both the structure and function of the hemolymph microbiota provided valuable insights into the mechanisms employed by the hemolymph microbiota of E. sinensis in response to bacterial infections. ABSTRACT: The Chinese mitten crab (Eriocheir sinensis) has significant economic potential in both the Chinese domestic and global markets. The hemolymph microbiota is known to play a critical role in regulating physiological and biochemical functions in crustaceans. However, the study of the hemolymph microbiota of E. sinensis in response to infections has not been undertaken. In this study, changes in the composition and function of the hemolymph microbiota in E. sinensis infected with either Staphylococcus aureus (Sa) or Aeromonas hydrophila (Ah) were investigated using 16S rRNA sequencing, with a phosphate buffer saline (PBS) injection serving as the control. Results showed that the dominant hemolymph microbiota of E. sinensis were Proteobacteria, Bacteroidota, and Firmicutes. The relative abundance of the phyla Firmicutes, Bdellovibrionota, and Myxococcota was significantly reduced in both Sa and Ah groups compared to the PBS group. At the genus level, compared to the PBS group, a significant increase in the abundance of Flavobacterium and Aeromonas was found in both Ah and Sa groups. The analysis of the functional profile showed that pathways related to ‘cell growth and death’, ‘metabolism of terpenoids and polyketides’, ‘cancers’, ‘lipid metabolism’, ‘neurodegenerative diseases’, ‘metabolism of other amino acids’, ‘xenobiotics biodegradation and metabolism’, and ‘circulatory system and endocrine system’ were predominant in the Ah group. Meanwhile, pathways related to ‘metabolism or genetic information progressing’, such as ‘translation’, ‘metabolic diseases’, and ‘cellular processes and signaling’, were enriched in the Sa group. This study revealed the effects of pathogens (S. aureus or A. hydrophila) on the maintenance of the hemolymph microbiota in E. sinensis. It shed light on the mechanisms employed by the hemolymph microbiota of E. sinensis under pathogen stimulation.