Arzul, I. | bioRxiv Science

bioRxiv2023

Genetic differentiation and host specialization among OsHV-1 infecting two oyster species in France

AbstractCross-species transmission is a major driver of disease emergence in humans and animals. The Ostreavirus ostreidmalaco1 (OsHV-1) is mainly associated with mortality in the Pacific oyster Magallana gigas, but has also been found in other mollusks, including the European flat oyster Ostrea edulis. This raises questions about OsHV-1 host specificity. This study explored the genetic differentiation of OsHV-1 in M. gigas and O. edulis and the underlying mechanisms. Using high-throughput sequencing, 40 OsHV-1 genomes were obtained from both O. edulis and M. gigas and were analyzed to assess viral diversity, lineage isolation, and cross-species transmission. Comparative genomics, population genetics, phylogenetic and phylodynamic methods revealed that host species significantly influence viral genetic structure. The data suggest that OsHV-1 was introduced in Europe with M. gigas, followed by a cross-species transmission event and divergence into two distinct lineages. Selection signals were identified in genomic regions involved in key viral functions, including host binding, DNA replication, and membrane-associated proteins, indicating possible adaptation to different hosts. Future research should investigate coevolution between OsHV-1 and a broader range of host species using phylogenetic approaches to better understand host-virus dynamics.

evolutionary biology↗

bioRxiv2022

Emergence and clonal expansion in Europe of Vibrio aestuarianus lineages pathogenic for oysters

Crassostrea gigas oysters represent a significant global food source, with 4.7 million tons harvested per year. In 2001, the bacterium V. aesturianus francensis emerged as a pathogen that causes adult oyster mortality in France and Ireland. Its impact on oyster aquaculture has increased in Europe since its reemergence in 2012. To better understand the evolutionary mechanisms leading to the emergence and persistence over time of this pathogen, we conducted a survey of mollusk diseases through national reference laboratories (NRLs) across Europe. We analyzed 54 new genomes of V. aestuarianus (Va) isolated from multiple environmental compartments since 2001, in areas with and without bivalve mortalities. We used a combination of comparative genomics and population genetics approaches to show that Va francensis lineages have undergone clonal expansion in Europe, likely after a recent selective bottleneck. Low mutation and recombination rates may have selected particular virulent genotypes. Furthermore, we identified a specific cus-cop-containing island conferring copper resistance to Va francensis whose acquisition may have favored the emergence of pathogenic lineages adapted to oysters.

microbiology↗