Composition and dynamics of Crassostrea gigas hemo-microbiota: microbial diversity, relationship with the oyster genetic background and the environment

Hemo-microbiota, Ifremer site policy 2015-16, CoDyVir, EMBRC France 2017
Massive mortalities of oysters are indicative of complex multifactorial diseases whose pathogenesis remains poorly understood. In addition, many studies are emerging today on the impact of species assemblages (holobionts) and their dynamics on the interaction of the meta-organism with the environment. In this context, the hemo-microbiota project proposes to use global approaches without a priori to characterize the entire microbial community (prokaryotes, protists and viruses) present within the hemolymph oysters. To this end, we used 5 families of oysters of different genetic backgrounds produced in hatchery. These 5 families were then transplanted into the natural environment during infectious and non-infectious periods. The microbial diversity of the hemolymph was then analyzed by high throughput sequencing approaches. These approaches allowed us to (i) characterize the structure and the dynamics of the 3 microbial communities and (ii) determine the influence of oyster’s genetic background and environmental microflora on the composition and dynamics of these communities.
The project has shown that the oyster hemolymph constitutes a complex and dynamic ecological niche. Indeed, the hemolymph hosts bacteria as already described but also protists and viruses. The acquisition of these microbial populations during the early stages of oyster development is virtually unaffected by the genetic background of animals, and environmental factors seem to dominate the establishment of this microbiota. The transplantation of oysters in natural environments during non-infectious and infectious periods shows that, once again, the environment plays a major role in the dynamics of the hemo-microbiota. However, during the infectious period, the genetic background of animals plays a key role in the dynamics of viral community living in oyster’s blood.