Microbial regulation of dissolved organic matter revealed by integrated metabolomics and metagenomics in the World's deepest blue hole.

Dissolved organic matter (DOM) is central to marine biogeochemical cycles, with its composition and dynamics closely linked to microbial communities. In oxygen-stratified extreme environments, however, the ecological relationships between DOM and microbes remain insufficiently explored. This study explores the dynamics of DOM and microbial communities in the Sansha Yongle Blue Hole, the world's deepest ocean blue hole, using an integrated metabolomics and metagenomics approach. Our findings elucidate significant alterations in microbial communities and DOM composition in response to variations in oxygen concentrations. Specifically, various DOM components, including dissolved organic sulfur (DOS) and dissolved organic nitrogen (DON), along with a spectrum of small molecule metabolites, were affected by microbial metabolic activities. Higher concentrations of DOS in the anoxic layer were positively correlated with increased sulfur metabolism in microbial communities, whereas lower concentrations of DON in the chemocline were associated with the coupling of nitrification and denitrification processes. Additionally, metabolites such as lipids, amino acids, isovalerylcarnitine, and peptides, associated with microbial physiological functions, energy metabolism, and signal transduction processes, varied with oxygen stratification. These findings contribute to a deeper understanding of the intricate relationships between microbial communities and DOM dynamics in extreme marine environments.