Abstract
Associations between micro- and macro-organisms (forming holobionts) are common and mostly specific in nature. Although microbes might contribute to the holobiont homeostasis, their role in the adaptive capacities of the holobiont remains unclear in most of the living species, and studies testing the links between host fitness and microbiota characteristics are still lacking.
To tackle this issue, we analyzed the microbiota of full-sib progenies from five biparental oyster families in a controlled condition (hatchery) and after transplantation during non-stressful or stressful periods in two geographic regions (Atlantic Ocean and Mediterranean Sea). We used 16S rRNA gene-metabarcoding to study taxonomic compositions of microbial communities. First, comparisons of microbial assemblages showed that environmental conditions highly influenced oyster microbiota. However, different ecological niches existed between oyster tissues and seawater, and even between the five families. Secondly, because two oyster families displayed high mortalities in both stressful periods, we compared their microbiota characteristics to the three other families. All oyster microbiota were highly modified after transplantation and no clear microbiota dysbiosis was observed for the two susceptible families. Moreover, despite similar levels of mortalities in both geographic regions, we identified many differences of microbial assemblages between resistant and susceptible families in the Atlantic Ocean, but few in the Mediterranean Sea. Particularly, susceptible families showed lower diversity of their microbiota than the resistant ones in stressful periods. Secondly, we highlighted that microbiota of susceptible oyster families had higher variability than the resistant ones at the scale of bacterial orders, but also less variability at the scale of OTUs. Lastly, while resistant families had increased relative abundances of cyanobacteria (Subsection III, family I) during the stressful period, susceptible oysters had low stability of Rhodospirillales, Rhodobacterales, Flavobacteriaceae and Erythrobacteraceae.
This study highlighted links between microbiota diversity and low variability of microbial assemblages at higher taxonomic ranks with oyster mortalities. We also identified bacterial taxa related to oyster fitness.
