The relationship of nitrate reducing bacteria on the basis of narH gene sequences and comparison of narH and 16S rDNA based phylogeny.

On the basis of available nitrate reductase gene sequences primer pairs were designed to specifically amplify gene stretches of the beta-subunit of the membrane-bound nitrate reductase (narH). Additional sequences of this gene were amplified and sequenced from pure cultures of reference species and new isolates. The distribution and phylogeny of this gene in denitrifying and nitrate-reducing bacteria was analysed. Comparison of phylogenetic trees based on 16S rDNA sequences with those based on narH sequences revealed highly similar relationships of both genes from most of the bacteria analysed. Since highly conserved functional cysteine clusters within bacterial and archaeal narH sequences support a linear evolution from one common progenitor a long evolutionary history of the respiratory membrane-bound nitrate reductase can be inferred from our phylogenetic data.