Properties of universal primer pairs and their coverage for phylogenetic and environmental groupings in the nifH database.

aData indicate primer binding to specific groupings in the nifH phylogeny. Abbreviations are as follows: Alpha, Beta, and Gamma Proteobacteria (Pr); Cyanobacteria (Cy); Cluster III (III); Cluster IA (IA); Paenibacillus (Pb); Frankia (Fr); Epsilon Proteobacteria Containing Cluster (Ep); paralogous sequences in Cluster IV (IV). In some cases highly degenerate primers bind to multiple positions in the sequence generating coverage values that exceed 100%.bPrimer coverage queried against sequences recovered from specific environments (Environ.) as described in methods. Environments include: soils (Soil), microbial mats (Mat), and pelagic marine samples (Sea).cPosition of amplicon in nifH is relative to A. vinelandii nifH (Genbank ACCN# M20568).dLength expected for PCR amplicon.eData indicate primer binding with 0 mismatches to all nifH sequences in the database.NA Data not available as nucleotide information is not available for the target group in the region of primer binding.