Variability in the Composition of Pacific Oyster Microbiomes Across Oyster Families Exhibiting Different Levels of Susceptibility to OsHV-1 μvar Disease

Abstract

Oyster diseases are a major impediment to the profitability and growth of the oyster aquaculture industry. In recent years, geographically widespread outbreaks of disease caused by ostreid herpesvirus-1 microvariant (OsHV-1 μvar) have led to mass mortalities among Crassostrea gigas, the Pacific Oyster. Attempts to minimize the impact of this disease have been largely focused on breeding programs, and although these have shown some success in producing oyster families with reduced mortality, the mechanism(s) behind this protection is poorly understood. One possible factor is modification of the C. gigas microbiome. To explore how breeding for resistance to OsHV-1 μvar affects the oyster microbiome, we used 16S rRNA amplicon sequencing to characterize the bacterial communities associated with 35 C. gigas families, incorporating oysters with different levels of susceptibility to OsHV-1 μvar disease. The microbiomes of disease-susceptible families were significantly different to the microbiomes of disease-resistant families. OTUs assigned to the Photobacterium, Vibrio, Aliivibrio, Streptococcus, and Roseovarius genera were associated with low disease resistance. In partial support of this finding, qPCR identified a statistically significant increase of Vibrio-specific 16S rRNA gene copies in the low disease resistance families, possibly indicative of a reduced host immune response to these pathogens. In addition to these results, examination of the core microbiome revealed that each family possessed a small core community, with OTUs assigned to the Winogradskyella genus and the Bradyrhizobiaceae family consistent members across most disease-resistant families. This study examines patterns in the microbiome of oyster families exhibiting differing levels of OsHV-1 μvar disease resistance and reveals some key bacterial taxa that may provide a protective or detrimental role in OsHV-1 μvar disease outbreaks.

Microbiota Composition and Evenness Predict Survival Rate of Oysters Confronted to Pacific Oyster Mortality Syndrome

“…Furthermore, three bacterial families (Mycoplasmataceae, Rhodospirillaceae, and Vibrionaceae) were linked to susceptible oysters in hatchery and/or before disease development in the field, suggesting putative roles of opportunists or pathogens. Among Vibrionaceae, Photobacterium genus was mostly associated with S F32 in hatchery, and as well with low disease resistance oysters in a previous study (King et al, 2019). Among Rhodospirillaceae, Thalassospira genus was already identified in C. gigas oysters (Fernandez-Piquer et al, 2012).…”

Dynamics of the Pacific oyster pathobiota during mortality episodes in Europe assessed by 16S rRNA gene profiling and a new target enrichment next‐generation sequencing strategy

“…). Loss of microbiota diversity and proliferation of few OTUs (‘dysbiosis’) has previously been linked with impaired health in oysters (Green and Barnes, ; King et al ., ), including C . gigas (Garnier et al ., ; Lokmer and Wegner, ).…”

“…This may be linked to the filter feeding behaviour of oysters, which expose the animals to colonization by complex and highly variable microbial communities found in the seawater environment. Mycoplasmataceae, Arcobacter, Synechococcus and Spirochaetaceae dominated the microbiota in healthy (non-infected) oysters suggesting these taxa might play a beneficial role in oyster fitness and health status (King et al, 2019). Interestingly, Arcobacter and Mycoplasmataceae were found to represent an abundant fraction of the microbiota in the Eastern oyster (Crassostrea virginica) and Chilean oyster (Tiostrea chilensis) respectively, although their role within the host is still largely unknown (Romero et al, 2002;King et al, 2012).…”

“…1). Loss of microbiota diversity and proliferation of few OTUs ('dysbiosis') has previously been linked with impaired health in oysters (Green and Barnes, 2010;King et al, 2019), including C. gigas (Garnier et al, 2007;Lokmer and Wegner, 2015). It is thus apparent that specific microbial taxa and especially members of the Vibrio genus are likely to play a role in affecting oyster health status during disease outbreaks.…”

Diversity and Function of the Eastern Oyster (Crassostrea virginica) Microbiome

“…hemolymph, gill, mantle, and gut) when compared with microbial communities of the surrounding seawater, suggesting potential host selections that lead to the enrichment of specific groups [20]. Multiple factors, including changes in environmental conditions [15,17,21,22], diet [23], infection [24][25][26], and the use of probiotics [27], have been shown to influence the composition of oyster microbiomes during certain life stages and among different tissue types. All these studies set the stage for further investigating the taxonomic composition and functional potentials of the oyster microbiomes across different tissues.…”