Study on the Amphibious Adaptability of Mudskippers Based on Intestinal Metagenome

Objective In this study, we report the adaptability of two representative amphibian species, blue-spotted mudskipper (Boleophthalmus Periophthalmodon, BP) and giant-fin mudskipper (Periophthalmus magnuspinnatus, PM) to live on land, with a view to revealing the key role of gastrointestinal microbiota in the adaptation and specific immunity of mudskippers to amphibious life.

Method By using 16S amplicon sequencing and metagenomic tec hniques, the microbial composition, diversity, abundance and function of the intestines of amphibian and aquatic fish species were compared. The metagenomic data were utilized to compare two representative mudskippers (BP, PM) and three typical aquatic fish species including Ctenopharyngodon idella (CI), Hypophthalmichthys molitri (HM) and Aristichthys nobilis (AN) and the potential terrestrial marker gastrointestinal microbiota in mudskippers were investigated. In addition, the representative data of gastrointestinal microbiota from marine fish, freshwater fish, amphibians and terrestrial animals were obtained through extensive literature to compare the composition and function of intestinal microbiota in mudskippers.

Result Firmicutes, Proteobacteria, Bacteroidetes and Fusobacteria were dominant in the gastrointestinal microbiota of mudskippers. The contents of various dominant phyla were strikingly different among BP, PM and aquatic fishes. Th e most significant difference in the gastrointestinal microbiota between the two groups was the proportion of CKC4, a gastrointestinal bacterial phylum that is speculated to be related to host lipid metabolism, which ranged from 4% to 27% in CI, HM, AN but was not found in the mudskipper. In addition, the gastrointestinal microbiota of mudskipper containeds typical bacterial families in terrestrial animals, freshwater and seawater fishes fish and amphibians, which was consistent with their life characteristics at the salt-water interface between water and land. It was also observed that fishes had a higher proportion of Clostridium and Proteobacteria than terrestrial animals, which had more Bacteroides species. More interestingly, certain bacteria strains like S24-7, previously thought to be specific in terrestrial animals, were also identified in both BP and PM.

Conclusion The results suggest that the gastrointestinal microbial communities of mudskipper are more complex and diverse than those of aquatic fishes, which subsequently stimulate the host to form innate immune receptor gene families with higher diversity and more copy numbers through pathogen-related molecular pattern (PAMP) to a more complicated amphibian environment.