The Sydney rock oyster microbiota is influenced by location, season and genetics

Queensland unknown (QX) disease is a significant cause of economic loss for the Sydney rock oyster (SRO) aquaculture industry. Evidence is emerging that QX disease is multi-factorial in nature, with a number of environmental and host factors contributing to disease dynamics. Efforts to mitigate the impacts of QX disease are primarily focused on breeding for disease resistance however, the mechanisms that drive disease resistance are poorly understood. One potential factor influencing disease resistance is the microbiota. To determine the influence of location, season and disease resistance on the SRO microbiota, we used 16S rRNA (V1 – V3 region) amplicon sequencing. The microbiota of six SRO families with two categorised as QX-resistant and four as QX-susceptible, deployed to two different locations (Port Stephens and Wallis Lake, NSW, Australia) and over two seasons (Austral summer and winter), were characterised. As expected, the SRO microbiota was distinct to the microbial community found in seawater. Further, the SRO microbiota was significantly influenced by location and season, with operational taxonomic units (OTUs) assigned to the Candidatus Hepatoplasma and Endozoicomonas genera identified as significant drivers of microbiota dissimilarity between locations and seasons. Disease resistance also significantly influenced the SRO microbiota but only at the winter time point which is before the typical QX disease period. Overall, OTUs assigned to the Mycoplasma, Borrelia and Endozoicomonas genera were over-represented in QX-resistant SRO microbiota, whereas members of the Pseudoalteromonas, Vibrio, and Candidatus Hepatoplasma genera were over-represented in QX-sensitive microbiota. These findings confirm the influencing role of location and season on the microbiota structure as evidenced in other molluscan species, but also provide preliminary evidence that the microbiota assemblage before the QX disease period may be important for resistance to disease and may provide new avenues for managing SRO aquaculture in the future.