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A SitABCD homologue from an avian pathogenic Escherichia coli strain mediates transport of iron and manganese and resistance to hydrogen peroxide

Institut National de la Recherche Scientifique, INRS-Institut Armand-Frappier, 531 boul. des Prairies, Laval, Québec, Canada H7V 1B7

Correspondence
Charles M. Dozois
charles.dozois{at}iaf.inrs.ca

An operon encoding a member of the family of ATP-binding cassette (ABC) divalent metal ion transporters, homologous to Salmonella enterica SitABCD, has been identified in the avian pathogenic Escherichia coli (APEC) strain 7122. The sitABCD genes were located on the virulence plasmid pAPEC-1, and were highly similar at the nucleotide level to the chromosomally encoded sitABCD genes present in Shigella spp. A cloned copy of sitABCD conferred increased growth upon a siderophore-deficient E. coli strain grown in nutrient broth supplemented with the chelator 2,2'-dipyridyl. Ion rescue demonstrated that Sit-mediated growth promotion of this strain was due to the transport of iron. SitABCD mediated increased transport of both iron and manganese as demonstrated by uptake of ⁵⁵Fe, ⁵⁹Fe or ⁵⁴Mn in E. coli K-12 strains deficient for the transport of iron (aroB feoB) and manganese (mntH) respectively. Isotope uptake and transport inhibition studies showed that in the iron transport deficient strain, SitABCD demonstrated a greater affinity for iron than for manganese, and SitABCD-mediated transport was higher for ferrous iron, whereas in the manganese transport deficient strain, SitABCD demonstrated greater affinity for manganese than for iron. Introduction of the APEC sitABCD genes into an E. coli K-12 mntH mutant also conferred increased resistance to the bactericidal effects of hydrogen peroxide. APEC strain 7122 derivatives lacking either a functional SitABCD or a functional MntH transport system were as resistant to hydrogen peroxide as the wild-type strain, whereas a sit mntH double mutant was more sensitive to hydrogen peroxide. Overall, the results demonstrate that in E. coli SitABCD represents a manganese and iron transporter that, in combination with other ion transport systems, may contribute to acquisition of iron and manganese, and resistance to oxidative stress.

The GenBank/EMBL/DDBJ accession numbers of the SitABCD-encoding DNA region of pAPEC-1 from strain 7122, and the sitA gene from E. coli CFT073 sequenced from plasmid pIJ4, are AY598030 and DQ256074, respectively.

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