Lucasson, A. | bioRxiv Science

bioRxiv2020

A core of functionally complementary bacteria colonizes oysters in Pacific Oyster Mortality Syndrome.

BackgroundThe Pacific oyster Crassostrea gigas is one of the main cultivated invertebrate species worldwide. Since 2008, oyster juveniles have been confronted with a lethal syndrome known as the Pacific Oyster Mortality Syndrome (POMS). POMS is a polymicrobial disease initiated by a primary infection with the herpesvirus OsHV-1 Var that creates an oyster immunocompromised state and evolves towards a secondary fatal bacteremia. In the present article, we describe the implementation of an unprecedented combination of metabarcoding and metatranscriptomic approaches to show that the sequence of events in POMS pathogenesis is conserved across infectious environments. We also identified a core bacterial consortium which, together with OsHV-1 Var, forms the POMS pathobiota. This bacterial consortium is characterized by high transcriptional activities and complementary metabolic functions to exploit hosts resources. A significant metabolic specificity was highlighted at the bacterial genus level, suggesting low competition for nutrients between members of the core bacteria. Lack of metabolic competition might favor complementary colonization of host tissues and contribute to the conservation of the POMS pathobiota across distinct infectious environments.

microbiology↗

bioRxiv2018

Diversity and stability of microbiota are key factors associated to healthy and diseased Crassostrea gigas oysters

Pacific Oyster Mortality Syndrome (POMS) affects Crassostrea gigas oysters worldwide and caused important economic losses. Disease dynamics was recently deciphered and revealed a multiple and progressive infection caused by the Ostreid herpesvirus OsHV-1 {micro}Var, triggering an immunosuppression followed by microbiota destabilization and bacteraemia by opportunistic bacterial pathogens. However, it remains unknown if microbiota might participate to oyster protection to POMS, and if microbiota characteristics might be predictive of oyster mortalities. To tackle this issue, we transferred full-sib progenies of resistant and susceptible oyster families from hatchery to the field during a period in favour of POMS. After five days of transplantation, oysters from each family were either sampled for individual microbiota analyses using 16S rRNA gene-metabarcoding or transferred into facilities to record their survival using controlled condition. As expected, all oysters from susceptible families died, and all oysters from the resistant family survived. Quantification of OsHV-1 and bacteria showed that five days of transplantation was long enough to contaminate oysters by POMS, but not for entering the pathogenesis process. Thus, it was possible to compare microbiota characteristics between resistant and susceptible oyster families at the early steps of infection. Strikingly, we found that microbiota evenness and abundances of Cyanobacteria (Subsection III, family I), Mycoplasmataceae, Rhodobacteraceae, and Rhodospirillaceae were significantly different between resistant and susceptible oyster families. We concluded that these microbiota characteristics might predict oyster mortalities.

microbiology↗