Figure 7.

Selected processes throughout the water column. The biodiversity increased along the depths increased. The genome size of MAGs at ≥4000 m layers was slightly larger compared to those at 0–2000 m. Glycoside hydrolases (GHs) and Polysaccharide lyases (PLs) had inverse vertical variation patterns, showing a generally declining and increasing trend with depth, respectively. Microorganisms in >10,000 m waters utilize alkanes more than aromatics, with the opposite occurring in 0–9600 m waters. Microorganisms at 0–2000 m are more inclined to use the dissimilatory sulfate reduction pathway, while microorganisms at ≥4000 m are more inclined to use the assimilatory sulfate reduction pathway. In surface waters, the relative abundance of genes for photosynthesis and CBB cycle was enriched, and thus provides the main source of primary production. In addition, glycosyltransferases (GTs) occupied the highest proportion at the surface layer compared to other depths, indicative of a higher potential of carbohydrate biosynthesis in this environment. Glycolysis was most abundant in surface waters. The deepest waters (>10,000 m) are enriched for DNRA, nitrogen fixation and urea transport, which could provide an additional ammonia source for ammonia oxidation and survival of the α lineage of the AOA. Additionally, microbial activities may be enhanced at >10,000 m with a higher relative abundance of proteins involved in oxidative phosphorylation and the glyoxylate shunt.