Bacteria profile of water and gills of Mytilus galloprovincialis from a North Italian lagoon

This study aimed to assess the microbiota in water and gills of Mytilus galloprovincialis collected at Scardovari lagoon (Po Delta, Italy). The seasonal and spatial dynamics microbial communities were investigated with a DNA metabarcoding approach, which simultaneously amplifies seven hypervariable regions of the bacterial 16S rRNA gene. Mussels and water were sampled in two areas of the lagoon (North-West and South-East) three times between April and June 2021. The most abundant bacterial taxa (Methylobacterium, Burkholderia, and Sphingomonas) in gill tissue found by DNA metabarcoding were confirmed using Sanger analysis and qPCR. Our results highlight a characteristic bacterial profile in mussels compared to water and the Principal Component Analysis (PCA) revealed the presence of separate community structures within gills and water samples. In gills tissues, the families of Sphingomonadaceae, Beijerinckiaceae, and Burkholderiaceae were abundant, while in seawater samples Rhodobacteraceae, Flavobacteriaceae, and Microbacteriaceae families were the most represented. The gills of mussels sampled in the northern and southern areas presented a high similarity of microbial communities. The seasonal dynamic revealed structural variation of bacterial profile and alfa-diversity composition both in gills and water (P<0.05) and the unique presence of some pathogenic bacteria orders was highlighted in May and June when temperature raised. These findings enhance our understanding of the gill-associated microbiota with a space and time microbiota analysis approach. The relationship of gill bacteria communities with the surrounding environment was pointed out, enabling the development of a transferable method to other economically important seafood.