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J. Bacteriol., 06 1995, 3004-3009, Vol 177, No. 11
M Mills and SM Payne
Shigella species can use heme as the sole source of iron. In this work, the
heme utilization locus of Shigella dysenteriae was cloned and
characterized. A cosmid bank of S. dysenteriae serotype 1 DNA was
constructed in an Escherichia coli siderophore synthesis mutant incapable
of heme transport. A recombinant clone, pSHU12, carrying the heme
utilization system of S. dysenteriae was isolated by screening on iron-poor
medium supplemented with hemin. Transposon insertional mutagenesis and
subcloning identified the region of DNA in pSHU12 responsible for the
phenotype of heme utilization. Minicell analysis indicated that a 70-kDa
protein encoded by this region was sufficient to allow heme utilization in
E. coli. Synthesis of this protein, designated Shu (Shigella heme uptake),
was induced by iron limitation. The 70-kDa protein is located in the outer
membrane and binds heme, suggesting it is the S. dysenteriae heme receptor.
Heme iron uptake was found to be TonB dependent in E. coli. Transformation
of an E. coli hemA mutant with the heme utilization subclone, pSHU262,
showed that heme could serve as a source of porphyrin as well as iron,
indicating that the entire heme molecule is transported into the bacterial
cell. DNA sequences homologous to shu were detected in strains of S.
dysenteriae serotype 1 and E. coli O157:H7.
Copyright © 1995, American Society for Microbiology
Genetics and regulation of heme iron transport in Shigella dysenteriae and detection of an analogous system in Escherichia coli O157:H7
Department of Microbiology, University of Texas at Austin 78712, USA.
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