Bivalves maintain a core gut microbiome: seasonal trends and species variation

Melissa L. Pierce* and J. Evan Ward
University of Connecticut, Dept. Marine Sciences
1080 Shennecossett Rd.
Groton, CT 06340
melissa.pierce@uconn.edu

In this seasonal study, differences in gut bacterial communities were evaluated between two species of bivalves, the eastern oyster (Crassostrea virginica) and the blue mussel (Mytilus edulis) collected from Long Island Sound, Connecticut. Marine snow and aggregate-free seawater (AFSW) were also collected. Both genetic and functional diversity of the samples were assessed. Biolog EcoPlates provided community-level physiological profiles (CLPPs) using carbon substrates, a subset of functional diversity. 16S rRNA gene sequencing (Illumina MiSeq) of the V4 region was used to evaluate microbiome community composition. Similarity Percentage (SIMPER) analysis of 16S sequencing data indicated that oysters and mussels maintain highly similar gut microbiomes, with some temporal variation (Table 1). Data from EcoPlates showed that bivalve gut bacterial communities differ from one another and vary temporally (Table 1). Additionally, mussel bacterial communities maintained high richness and evenness values throughout the year, even when the food source (marine snow) and AFSW values dropped. Oyster microbiomes, however, exhibited functional plasticity, with significant differences in the types of carbon substrates utilized seasonally. Results of further work, which isolated oysters in sterile microcosms in order to elucidate the dynamics of transient vs. resident gut bacteria and their relationship to the core microbiome, will also be presented. Microcosm oysters had gut community CLPPs that were not significantly different from those present in the natural environment, indicating that transient bacteria may not contribute to the functional diversity of these communities.