Geographic origin and host’s phylogeny are predictors of the gut mucosal microbiota diversity and composition in Mediterranean scorpionfishes (Scorpaena sp.)

Abstract Background The gut microbiome holds an important role in the health and homeostasis of fishes. However, despite the large diversity and distribution of this vertebrate group, only the intestinal microbiome of a limited number of freshwater and marine fish species has been well characterized to date. Mediterranean scorpionfishes ( Scorpaena sp ) have a high commercial value in the Mediterranean Sea and Scorpaena scrofa is a candidate to become an aquaculture-reared species in a near future. However, this fish group is underrepresented in studies about fish gut microbiome. Results In this study, we characterized the gut mucosal microbial communities of three Scorpaena sp (n = 125) by using a comprehensive comparative dataset including 16S rRNA gene amplicon data from four different locations in the Mediterranean Sea. We report that in this fish group, geographical origin influences the diversity and the composition of the gut microbial communities more than host’s phylogenetic relatedness. Moreover, we observe a positive correlation between the composition of the gut microbiota and the phylogenetic distance between the hosts (i.e. phylosymbiosis). Finally, the core microbiota of each species was described both regionally and across the Mediterranean Sea. When investigated regionally, the core microbiota was characterized by bacterial genera holding important functions for the health and homeostasis of the host. By expanding the analysis to a broader geographical scale, a reduction in the size of the core microbiota of each species was observed and Clostridium senso stricto 1 appeared to be the only resident bacterial genus in the core gut microbiota of Scorpaena sp in the Mediterranean Sea. Conclusion This study reveals that the microbiota associated with the gut mucosa of scorpionfishes is not stable across the Mediterranean Sea and its composition depends on the fish population analyzed. Therefore, it highlights the importance of investigating the gut microbiome through the geographical range of a species and it suggests this as a general procedure to better characterize the gut microbial ecology of each fish species