Geographic Differences in the Gut Microbiome of the Eastern Oyster Crassostrea virginica

Oysters are an ecologically and commercially important species in estuarine environments, providing numerous ecosystem services such as the cycling of particulate matter, benthic-pelagic coupling, and exerting top-down control on phytoplankton communities. Oysters filter large quantities of water and, therefore, their gut tissues come into contact with large numbers of both free-living and particle-associated compounds and microbes. To better understand the oyster microbiome and its potential functional significance, we dissected the gut of eastern oysters from several different commercial fishery environments in Florida, Connecticut, and Maine and sequenced the V4 region of the 16S rRNA gene to determine microbial taxonomic composition. Samples included oysters housed in hatcheries (FL), cages (FL and ME), and maintained beds (CT). Microbiomes from both diploid and triploid oysters were investigated. Analysis of 16S rRNA gene sequences indicated that Mycoplasmatales dominated almost all oyster gut samples. Members of the Flavobacteriales and Spirochaetales were also consistently present as well as cyanobacteria. Sequence alpha diversity was highest in samples obtained from Florida. Ordination plots indicated that microbial communities were more similar in oysters obtained from the same location than those from sites in other states. No differences in microbial community structure were observed between diploid and triploid oysters. Future analysis will investigate temporal and geographic differences in the oyster gut microbiome.