Impacts of Nutrient Enrichment on Oyster Gut and Shell Microbiomes

As keystone species in the coastal environment, oysters play a crucial role in nitrogen cycling, improving water quality for other marine organisms and humans. It is understood that host-associated microbes are responsible for the oyster's ability to promote nitrogen cycling within the environment. However, the composition of oyster-associated microbiomes and their physiological mechanisms driving nitrogen cycling and gas production are unknown. Adult oysters (30 oysters per container, 6 containers) were deployed for three months in the summer of 2017 at two sites in Point Judith Pond, Rhode Island, with different levels of ambient nitrogen loading. Within each site, three of the six containers were spiked with fertilizer to simulate nutrient runoff. Tissues (gut, inner and outer shell biofilms) from a subsample of oysters (n=36, 3 per container) were collected for analysis of microbial community composition and function. The microbial community structures were determined by DNA amplification and sequencing of the 16S rRNA V6 region (n=108), and metatranscriptomes were sequenced from oyster pools per bucket (n=36) to determine the transcriptional response of the oysters to nutrient enrichment.