A multi-study analysis of gut microbiome data from the blue mussel (Mytilus edulis) emphasizes the methodological impact of gut voidance on biological interpretation

The blue mussel (Mytilus edulis) is a model organism used in a number of gut-microbiome surveys. Although raw 16S sequence data are often publicly available, unifying secondary analyses are lacking. The present work analyzed raw data from seven projects conducted by one group over seven years. Although each project had different motivations, experimental designs, and conclusions, all selected samples were from the guts of M. edulis collected from a single location in Long Island Sound. The goal of this analysis was to determine which independent factors (e.g., collection date, depuration status) were responsible for governing composition and diversity in the gut microbiomes. Results indicated that whether mussels had undergone depuration, defined here as voidance of feces in a controlled, no-food period, was the primary factor that governed gut microbiome composition. Gut microbiomes from non-depurated mussels were mixtures of resident and transient communities and were influenced by temporal factors. Resident communities from depurated mussels were influenced by final food source and length of time host mussels were held under laboratory conditions. These findings reinforce the paradigm that gut microbiota are divided into resident and transient components and suggest that future research efforts should consider the biological implications of gut sampling strategies.