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

William L King,Michael Dove,Wayne O’Connor,Nathan L R Williams,Justin R Seymour,Khue Viet Nguyen,Tim Kahlke,Maurizio Labbate,Nachshon Siboni,Cheryl Jenkins

doi:10.3389/fmicb.2019.00473

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.

Highlights

The Pacific oyster, Crassostrea gigas is a globally cultivated oyster species, but the cultivation of this species has been increasingly impacted by disease events (Azéma et al, 2015)
We have shown that the microbiome of C. gigas displays significantly different microbial assemblage structure according to oyster disease-resistance
This study provides insights into the C. gigas microbiome within the context of oysters bred for disease-resistance and highlights the potential involvement of the oyster microbiome in disease-resistance

Summary

Introduction

The Pacific oyster, Crassostrea gigas is a globally cultivated oyster species, but the cultivation of this species has been increasingly impacted by disease events (Azéma et al, 2015). A major pathogen of C. gigas is the ostreid herpesvirus 1 (OsHV-1), and its micro variant form (OsHV-1 μvar) (Davison et al, 2005; Segarra et al., 2010) This virus has caused severe mortality outbreaks over the last two decades (Friedman et al, 2005; Burge et al, 2006; Segarra et al, 2010; Jenkins et al, 2013; Mortensen et al, 2016), with some outbreaks resulting in over 90% mortality and leading to the death of many millions of oysters (ASI, 2015). Breeding programs generally involve breeding oyster genetic lines that have greater survival rates following exposure to OsHV-1

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