Figure 2.

Phylum-level taxonomic distribution of eight common functional genes detected in the subsurface metagenomes. N denotes the total number of gene sequences detected in the metagenomes. The taxonomic classification of these sequences was assigned based on the lineage of their NR-best hit. The common functional genes are denoted by letters: a: NarV gene; b: NPD gene; c: PAPS reductase gene; d: NifH gene; e: NifD gene; f: NifK gene; g: NifE gene; h: NifN gene. Sequence counts were also overlain with scaled color intensity for visual effect. The last row gives the number of phyla represented by each common functional gene.