Comparison of Gut Bacterial Communities in the Freshwater Mussel Sinanodonta woodiana at Different Life Stages

Freshwater mussels hold significant ecological and economic value. Gut bacterial communities can regulate the growth and immunity of freshwater mussels. However, the dynamics of gut bacterial communities in freshwater mussels at different life stages are still limited. This study used the globally widespread mussel, Sinanodonta woodiana, as a model animal and employed 16S rRNA sequencing technology to comparatively analyze the gut bacterial communities of early juveniles, late juveniles, and adults. Alpha diversity indices indicated a trend of increasing richness and diversity of the gut bacterial communities with the mussel growth. Beta diversity analysis revealed distinct stage-specific taxonomic profiles. At the phylum level, four dominant phyla were identified in the early juveniles, namely Fusobacteriota, Verrucomicrobiota, Pseudomonadota, and Cyanobacteriota; and seven dominant phyla were identified in both late juveniles and adults, namely Fusobacteriota, Pseudomonadota, Verrucomicrobiota, Cyanobacteriota, Bacillota, Bacteroidota, and Chloroflexota. Among them, the relative abundance of Fusobacteriota decreased with the mussel growth (p < 0.05), while the relative abundances of Pseudomonadota and Cyanobacteriota increased with the mussel growth (p < 0.05). At the genus level, four dominant genera were identified in the early juveniles: Cetobacterium, LD29, Cyanobium_PCC-6307, and Cupriavidus; seven dominant genera were identified in the late juveniles: Cetobacterium, Roseomonas, LD29, Cyanobium_PCC-6307, Limnolyngbya_CHAB4449, Terrimicrobium, Limnothrix; and nine dominant genera were detected in the adults: Cetobacterium, LD29, Roseomonas, Cyanobium_PCC-6307, Limnothrix, Limnolyngbya_CHAB4449, Sediminibacterium, Terrimicrobium, Acidibacter. Among these, the relative abundance of Cetobacterium decreased with the mussel growth (p < 0.05), while the relative abundance of Acidibacter increased with the mussel growth (p < 0.05). Functional prediction revealed that the gut bacterial communities were primarily involved in metabolic pathways, including the biosynthesis of ansamycins, biosynthesis of vancomycin group antibiotics, D-glutamine and D-glutamate metabolism, biotin metabolism, valine, leucine and isoleucine biosynthesis, and fatty acid biosynthesis. The findings provide insights for enhancing the nutrition and health of freshwater mussels.