NUCLEOTIDE-SEQUENCE ANALYSIS AND POTENTIAL ENVIRONMENTAL DISTRIBUTIONOF A FERRIC PSEUDOBACTIN RECEPTOR GENE OF PSEUDOMONAS SP STRAIN M114

The nucleotide sequence of the Pseudomonas sp. strain M114 pbuA gene, encoding the outer membrane receptor for ferric pseudobactin M114, has been determined. The region sequenced spans 2788 bases of plasmid pCU P3, within which the receptor gene had previously been localised. A si ngle open reading frame, potentially encoding 826 amino acids and incl uding a leader peptide of 44 amino acids, is evident and is followed b y an inverted repeat segment, which may act as a transcriptional termi nator. A 20 bp region of DNA, having significant homology with the E. coli Fur-binding consensus sequence, is located upstream of the open r eading frame. PbuA displays characteristics in common with other outer membrane proteins and displays strong homology with the TonB boxes of both E. coli and Pseudomonas receptors. More extensive homologies wer e found with the PupA receptor of P. putida WCS358 and the FhuE and Bt uB receptors of E. coli. It is suggested that areas exhibiting the lea st homology between these receptors may represent ferric siderophore-s pecific recognition sites of the PbuA protein. The deduced amino acid sequence of pbuA was compared with that of pupX, encoding the outer me mbrane receptor for ferric pseudobactin B10, of Pseudomonas sp. strain B 10. A direct alignment of the two proteins gave an identity score o f 92.5%. The distribution of PbuA-like receptors among Pseudomonas iso lates was investigated by DNA-DNA hybridisation analysis. The results suggest that a PbuA-like receptor may be widely distributed among Pseu domonas rhizosphere isolates.