The gut microbiome of freshwater mussels (Lampsilis ornata and Lampsilis ovata) after placement into the Tennessee and Mobile River Basins

Freshwater mussels are endangered fauna that can be impacted by environmental perturbations. The gut microbiome of freshwater mussels varies by locality and environmental conditions, but implications for mussels introduced into new rivers are unclear. Using mussel silos containing hatchery-propagated juvenile mussels, the effects of the environment on the freshwater mussel gut microbiome were assessed for two mussel species in two rivers in each of two river basins (Lampsilis ovata in the Tennessee River Basin, Lampsilis ornata in the Mobile River Basin). Juvenile mussels were placed in silos for eight weeks, after which a subset were used for microbiome analysis, a subset remained in silos, and another subset were reciprocally transplanted between rivers in that basin for a further eight weeks. After the initial eight weeks, mussels showed increased gut bacterial species richness, and distinct community composition compared to hatchery mussels. By 16 weeks, the gut microbiome of mussels remaining in their original river had become less diverse, while diversity metrics for transplanted mussels resembled that of week 8 mussels. In addition, reciprocally transplanted mussels had gut bacterial communities resembling mussels placed into and collected from the recipient river at 16 weeks. All mussels after eight weeks showed high proportions of Firmicutes in their gut microbiome, suggesting a developmental dependency of this phyla in the gut of Lampsilis species. These findings highlight the relationship between the environment and gut microbiome development in freshwater mussels, offering valuable insights into their adaptability and conservation strategies.