FIRST CHARACTERIZATION OF THE MICROBIAL COMMUNITIES OF THE BLUE HOLE OF FAANU MUDUGAU, MALDIVES

Abstract

Blue holes are vertical water-filled openings in carbonate rock that exhibit complex morphologies, ecologies, and water chemistry. To date, the Faanu Mudugau Blue Hole in the Maldives is the only known blue hole in the Indian Ocean. It opens on a lagoon floor at 30 m depth and descends to 85 m. A transition zone occurs at about 50 m, where temperature, salinity, pH and oxygen decrease, while both carbon dioxide and hydrogen sulphide increase considerably. The compositions and functions of the microbial communities inhabiting this blue hole are still poorly studied. We analysed the prokaryotes communities from water samples and from a microbial filamentous structure attached to the sidewall. Molecular and metabolic analyses were carried out. Four zones with different depth-related microbial communities were identified. A strong metabolic response was observed along the entire water column. The oxic-anoxic interface exhibited the highest microbial diversity and metabolic activity. In total, 48 metagenome-assembled genomes (MAGs) were recovered from the filamentous mat, predominantly composed of Chloroflexota, Proteobacteria, Desulfobacterota, and Planctomycetota phyla. However, none of these taxa have been classified to species level, suggesting the discovery of new uncharacterized species.