Fig. 2.

Arctic UCYN-A nifH sequences are identical to broadly distributed and abundant sequence types. Shown is a maximum likelihood phylogenetic tree of UCYN-A microdiversity based on partial nifH nucleotide sequences from a recent global survey (12). UCYN-A sequences from the Bering and Arctic Seas (red dots) are identical to dominant sequence types found in all major ocean basins. Regions where each sequence type has been found are specified by colored dots according to the legend; sequence counts from the global survey are also plotted. Nodes with bootstrap support >70 are identified with a diamond. Data from ref. 12.