Metabolic potentials of the gut microbes in Antarctic krill (Euphausia superba)

Antarctic krill (Euphausia superba) plays crucial roles in the Southern Ocean biological system, yet the ecological functions of their gut microbiota remain poorly understood. The study investigated the composition and diversity of the gut microbiota in E. superba using 16S rRNA gene sequencing, revealing a highly diverse and tissue-specific microbiota. Further investigation through direct metagenomics and culture-enriched metagenomics identified 12 metagenome-assembled genomes (MAGs), which might represent novel species based on their phylogenetic positions, average nucleotide identity (ANI), average amino acid identity (AAI), and relative evolutionary divergence (RED) values. These MAGs were grouped into two distinct clusters according to their completeness of metabolic modules. Although MAGs in cluster 2 showed lower read relative abundance compared to those in cluster 1, they exhibited a greater number of amino acid synthesis modules. The synthesis of glutathione, heme, ubiquinone, vitamins, and betaine by MAGs suggested potential roles in enhancing survival of E. superba in extreme environment. Moreover, the functional genes in the 12 MAGs had abundant transcripts indicating they exhibited high metabolic activity in the E. superba gut microbiota. These findings shed new light on the metabolic contributions of gut microbiota in E. superba.IMPORTANCEThis study provided a comprehensive characterization of the gut microbiome of Euphausia superba, revealing its diverse and functionally distinct microbial community. Furthermore, 12 metagenome-assembled genomes (MAGs) representing novel species were successfully identified. The metabolic analysis demonstrated that these microbes contribute to host nutrient acquisition by synthesizing essential amino acids and vitamins. The identification of antioxidant and osmoregulatory compound synthesis modules suggested that gut microbiota might facilitate the survival of E. superba in the harsh Antarctic environment. Those findings elucidated the host-microbe interactions in polar marine ecosystems and provided new insights into microbial contributions to host nutrient cycling and environmental adaptation in the Southern Ocean.