Spatial compartmentalization and temporal stability of associated microbiota in Pacific oyster Crassostrea gigas

The Pacific oyster Crassostrea gigas, one of the most exploited molluscs in the world, has suffered from massive mortality in recent decades, and the occurrence mechanisms have not been well-characterized. In this study, to reveal the relationship of associated microbiota to the fitness of oysters, temporal dynamics of microbiota in the gill, hemolymph, and hepatopancreas of C. gigas during April 2018–January 2019 were investigated by 16S rRNA gene sequencing. The microbiota in C. gigas exhibited tissue heterogeneity, of which Spirochaetaceae was dominant in the gill and hemolymph while Mycoplasmataceae enriched in the hepatopancreas. Co-occurrence network demonstrated that the gill microbiota exhibited higher inter-taxon connectivity while the hemolymph microbiota had more modules. The richness (Chao1 index) and diversity (Shannon index) of microbial community in each tissue showed no significant seasonal variations, except for the hepatopancreas having a higher richness in the autumn. Similarly, beta diversity analysis indicated a relatively stable microbiota in each tissue during the sampling period, showing relative abundance of the dominant taxa exhibiting temporal dynamics. Results indicate that the microbial community in C. gigas showed a tissue-specific stability with temporal dynamics in the composition, which might be essential for the tissue functioning and environmental adaption in oysters. This work provides a baseline microbiota in C. gigas and is helpful for the understanding of host-microbiota interaction in oysters.