Fig. 4

Functional characterization of genes carried by symbiont plasmids. a COG categories enriched in plasmid genes and metagenome-assembled genes. b Heatmap showing the relative gene frequency and mRNA expression patterns of plasmid genes in individual mussels collected from the hydrothermal vents (Daiyon-Yonaguni Knoll, DY; Iheya North Knoll, IN) and the methane seep (Formosa Ridge, FR). c Section showing gill filaments stained using FISH with the gene-specific probes sqr (green) and pmoA (red), followed by counterstaining with DAPI (blue). The sqr probe was ubiquitous in the bacteriocytes of the vent mussel (IN), while the pmoA probe was detected in both the vent (IN) and seep (FR) mussels. Scale bar: 50 μm