Contribution of Viral Genomic Diversity to Oyster Susceptibility in the Pacific Oyster Mortality Syndrome.

Jean Delmotte,Bruno Petton,Jean-Michel Escoubas,Pierre-Louis Stenger,Richard Galinier,Caroline Montagnani,Julien De Lorgeril,Guillaume Mitta,Cristian Chaparro,Delphine Destoumieux-Garzon,Yannick Gueguen,Jeremie Vidal-Dupiol

doi:10.3389/fmicb.2020.01579

Abstract

Juvenile Pacific oysters (Crassostrea gigas) are subjected to recurrent episodes of mass mortalities that constitute a threat for the oyster industry. This mortality syndrome named “Pacific Oyster Mortality Syndrome” (POMS) is a polymicrobial disease whose pathogenesis is initiated by a primary infection by a variant of an Ostreid herpes virus named OsHV-1 μVar. The characterization of the OsHV-1 genome during different disease outbreaks occurring in different geographic areas has revealed the existence of a genomic diversity for OsHV-1 μVar. However, the biological significance of this diversity is still poorly understood. To go further in understanding the consequences of OsHV-1 diversity on POMS, we challenged five biparental families of oysters to two different infectious environments on the French coasts (Atlantic and Mediterranean). We observed that the susceptibility to POMS can be different among families within the same environment but also for the same family between the two environments. Viral diversity analysis revealed that Atlantic and Mediterranean POMS are caused by two distinct viral populations. Moreover, we observed that different oyster families are infected by distinct viral populations within a same infectious environment. Altogether these results suggest that the co-evolutionary processes at play between OsHV-1 μVar and oyster populations have selected a viral diversity that could facilitate the infection process and the transmission in oyster populations. These new data must be taken into account in the development of novel selective breeding programs better adapted to the oyster culture environment.

Highlights

Bivalve mollusk culture is an important sector of world aquaculture, representing approximately a fifth of the global production with 15.7 million tons harvested in 2017 (FAO and WHO, 2018)
We further examined the distribution of all variants that occurred in open reading frames (ORFs) and we found that 299 Single Nucleotide Polymorphism (SNP) were located in ORFs
We found that 15 out of 19 ORFs encoding this type of proteins in the Ostreid herpesvirus 1 (OsHV-1) genome, contain at least one nsSNP and most of these mutations are specific to Atlantic or Mediterranean viral populations

Summary

Introduction

Bivalve mollusk culture is an important sector of world aquaculture, representing approximately a fifth of the global production with 15.7 million tons harvested in 2017 (FAO and WHO, 2018). The Ostreid herpesvirus (OsHV-1) is recognized as being responsible for sporadic mortalities in several bivalve mollusks but it is one of the main mortality threats for the most cultivated bivalve species, the Pacific oyster Crassostrea gigas (Arzul et al, 2001a; Renault et al, 2001; Davison et al, 2005; da Silva et al, 2008; Solomieu et al, 2015; Xia et al, 2015; Burge et al, 2018) In this bivalve species, OsHV-1 triggers the Pacific oyster mortality syndrome (POMS) that has plagued the oyster production worldwide, from Europe to north and south America and Asia, for more than a decade (Pernet et al, 2012; Hwang et al, 2013; Jenkins et al, 2013; Bai et al, 2015; Mortensen et al, 2016; Prado-Alvarez et al, 2016; Caceres-Martinez et al, 2018). The infectious process is completed with subsequent bacteraemia leading to oyster death (de Lorgeril et al, 2018)

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Discussion

Conclusion