Figure 1. Coverage of the nifH gene by sequences and primers in the nifH database.

The number of sequences in the nifH database is depicted in relation to alignment position along the gene. Alignment positions are referenced to the nifH nucleotide position from Azotobacter vinelandii (Genbank ACCN# M20568). Universal nifH primer sequences listed in Table 1 and 2 are indicated by grey horizontal lines.