Microbiology (1 998), 144,44 1-448 Printed in Great Britain Localization of denitrification genes on the chromosomal map of Pseudomonas aeruginosa

Cleavage of chromosomal DNA from Pseudomonas aeruginosa PA0 by Spel and DpnI has been used together with PFGE and Southern hybridization to establish the map location of the following principal denitrification genes: narGH (encoding the large and small subunits of respiratory nitrate reductase), nirS (cytochrome-cd, nitr i te reductase), nirE (uroporphyrinogen-Ill methyltransferase for haem d, biosynthesis), norCB (nitric-oxide reductase complex), nosZ (nitrous-oxide reductase) and nosA (an outer-membrane protein and OprC homologue). The study also included several genes related to anaerobic or microaerophilic metabolism: napA (encoding the catalytic subunit of the periplasmic nitrate reductase), ccoN (catalytic subunit of the cytochrome-cbb, oxidase), hemN (oxygen-independent coproporphyrinogen-Ill oxidase), an fnr-like regulatory gene, and azu and fdxA (electron carriers azurin and ferredoxin, respectively). Genes necessary for denitrif ication are concentrated at 20 to 36 min on the P. aeruginosa chromosome, where they form three separate loci, the nir-nor, nar and nos gene clusters. Genomic DNA of Pseudomonas stutzeri ZoBell was also subjected to Spel restriction and Southern analysis to assign denitrif ication genes to individual fragments. A homologue of nosA encoding a putative component of the Cu-processing apparatus for nitrous-oxide reductase was identified. In both P. aeruginosa and P, stutzeri there is evidence for the linkage of anr (fnrA) with hemN and ccoN; and for the presence of a napA gene