Hydrolytic Enzymes' Fingerprints in Surface and Deep-Sea Prokaryotic Communities in the Ross Sea: A Metagenomic Approach

The Ross Sea is characterized by a significant export of particulate organic carbon, with up to 50% of surface primary production being transferred to deep water layers. On their way to the ocean's interior, these particles undergo a remineralization process mainly carried out by prokaryotic communities through a complex set of hydrolytic enzymes. In this study, we used a metagenomic approach to explore the genetic repertoire of free-living and total prokaryotic communities at surface and in deep water masses of the Ross Sea. We focused on genes involved in the production of hydrolytic enzymes, including carbohydrate-active enzymes (CAZymes), proteases, and lipases. Our analysis revealed that the genetic profile of prokaryotes reflects different strategies for optimizing the degradation of organic substrates, adapting to variations in the quantity and quality of particulate organic matter along the water column, and at different locations. These results suggested that Ross Sea surface communities were strongly influenced by the dynamics of phytoplankton at different sampling sites, exhibiting greater variability in their enzymatic repertoire in respect to bottom communities. Deep-sea microbes, on the other hand, rely on a broader and more diverse set of enzymes compared to surface communities, being more adapted to a particle-bound lifestyle and playing a critical role in the remineralization of complex polysaccharides, such as algal cell wall components.