Methanotrophy dominated symbiosis in novel species Gigantidas niobengalensis from the cold seeps of K-G basin

Bathymodiolus mussels, which are prominent invertebrates at cold seeps and hydrothermal vents, are known for hosting symbiotic microbes within their gills. In this study, the microbial communities associated with the gills of novel bathymodioline mussel Gigantidas niobengalensis from an active cold seep site of K-G basin was investigated by 16S rRNA amplicon sequencing. The average abundance of culturable methanotrophs in the gill tissues was 3.4 ± 0.9 × 104 CFU g-1 with average methane oxidation rates of 1.71 ± 0.04 to 1.89 ± 0.02 µM g-1 d-1 under aerobic and 1.86 ± 0.001 to 1.98 ± 0.005 µM g-1 d-1 under anaerobic conditions. Metagenomic analysis revealed dominance of methanotrophs within the microbial communities comprising of >55% bacterial and >28% archaeal methanotrophs; with phyla Proteobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia, Actinobacteria, Euryarchaeota and Crenarcheaota being prevalent. Functional classification highlighted methane metabolism (20%) and carbon fixation (22%) as major energy metabolism pathways. This study represents the first metagenomic characterization of gill-associated symbionts in the novel cold seep mussel Gigantidas niobengalensis from the Indian Ocean. The findings fill a knowledge gap on chemosynthetic symbioses in Indian cold seep ecosystems and provide insights into metabolic adaptation of G. niobengalensis in the cold seep ecosystem.