The catA gene, encoding the major CatA from a root-colonizing isolate Pseudomonas putida (Pp), was cloned by complementation into a catalase (Cat)-deficient Escherichia coli (Ec) strain UM2. The ORF for catA consisted of 479 aa with a higher degree of identity with typical Cat from eukaryotes than prokaryotes. Chromosomal homologous exchange with a mutant gene bearing an insertion of a luxAB-npt cassette into the SfiI site of catA generated a CatA-deficient Pp isolate. This mutant and another mutant, J1M, derived by EMS mutagenesis, were highly sensitive to hydrogen peroxide. CatA activity and resistance to hydrogen peroxide were restored in both mutants by catA. Adjacent to the 3' end of catA was a potential ORF of 462 nt that had high identitity with other bfr genes that encode iron-storage proteins. Northern analysis of the bfr gene from Pp revealed a transcript of approximately 500 nt. CatA and bfr probes hybridized to the same size restriction fragments in genomic DNAs from other root-colonizing and plant pathogenic pseudomonads. Thus, the genes for an iron-storage protein and the heme-containing Cat appear to be conserved in adjacent loci in certain pseudomonads.