Diet-driven shifts in microbiome composition and predicted metabolic functions of Mytilus coruscus larvae

Different microalgal diets can shape the bacterial and fungal communities associated with mussel larvae. This study investigates the composition, diversity, and functional roles of bacterial and fungal communities in Mytilus coruscus planktonic larvae at the veliconcha stage, under different mixed microalgal diets. Mussel larvae were cultured under controlled conditions using two mixed diets: Isochrysis galbana + Rhinomonas reticulata (ISORHI) and I. galbana + Rhodomonas baltica (ISORHO). High-throughput sequencing revealed significant differences in the bacterial and fungal compositions between the two groups. The ISORHI group exhibited higher bacterial diversity, with Methylophaga and Marinobacter as dominant genera, while Roseovarius and Fusibacter dominated the ISORHO group. The ISORHI group also exhibited higher fungal diversity, whereas Aspergillus predominated in the ISORHO group. Functional predictions suggested that microbial communities in the ISORHI group may be more associated with carbon metabolism-related pathways, while larvae fed the ISORHI diet showed higher predicted representation of nitrogen and sulfur cycling pathways. The predicted differences suggest distinct functional potentials between the two dietary groups, though they do not represent direct measurements of metabolic activity. These findings reveal diet-induced shifts in larval microbial communities and provide a basis for future investigations into host-microbe-diet interactions in mussel aquaculture.