Cloning and characterization of an iron-uptake ATP-binding cassette (ABC) transporter of Bartonella henselae

Bartonella henselae is a fastidious gram-negative, slow-growing organism that is a main causative agent of cat scratch disease. Cat scratch disease is characterized by the presence of subacute regional lymphadenopathy following a cat scratch or bite. The objective of this study was to clone and characterize the heme receptor of B. henselae. However, the cloning and characterization of an iron-uptake ATP-binding cassette transporter, or ABC transporter, are reported. ABC transporters are responsible for transporting a variety of solutes across the cell membrane. This ABC transporter is possibly for ferrichrome, ferric dicitrate, ferric enterobactin, or hemin, and is probably part of an operon involved in uptake of one of these iron sources. Iron acquisition is important for many microorganisms, and is often a virulence factor in pathogenesis. Southern hybridization with Vibrio vulnificus heme receptor DNA, hupA, with the cosmid containing B. henselae DNA fragments resulted in nonspecific binding. Oligonucleotides were then constructed from highly conserved regions of bacterial species' heme receptor protein sequences. The DNA sequencing analysis of the clones homologous to the oligonucleotide hybridization revealed the VirB operon of B. henselae. However, a 753-bp open reading frame upstream from the VirB operon revealed homology to an iron-uptake ABC transporter. The iron-uptake ABC transporter of B. henselae has 46.8% identity and 73.4% homology with Bacillus halodurans ferrichrome ABC transporter. The protein is 251 amino acids in length with a predicted molecular weight of 29.266.77 g/mol and an isoelectric point (pI) of 9.30. The DNA sequence and protein analyses are reported in this document. Further sequencing upstream from the ABC transporter may reveal the heme receptor and other iron-uptake genes.