Figure 2.

Phylogenetic tree of the major Bohai Sea sediment NifH sequences constructed with the neighbor-joining method. The NifH sequences of the most abundant OTUs (no <5 clones) were used for tree construction. The tree branch distances represent the amino acid substitution rate, and the scale bar represents the expected number of changes per homologous position. Bootstrap values higher than 50% of 100 resamplings are shown near the corresponding nodes. The chlorophyllide reductase iron protein subunit BchX sequences from Rhodobacter capsulantus and R. sphaeroides were used as outgroup.