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 wer e designed to specifically amplify gene stretches of the P-subunit of the m embrane-bound nitrate reductase (narH). Additional sequences of this gene w ere 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 ba sed on 16S rDNA sequences with those based on narH sequences revealed highl y similar relationships of both genes from most of the bacteria analysed. S ince highly conserved functional cysteine clusters within bacterial and arc haeal narH sequences support a linear evolution from one common progenitor a long evolutionary history of the respiratory membrane-bound nitrate reduc tase can be inferred from our phylogenetic data.