Heme as an iron source in Sinorhizobium meliloti

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DESCRIPTION (provided by applicant): In addition to its many cellular functions, heme is also a source of nutritional iron for many bacteria. The acquisition and metabolism of heme is essential for virulence in bacterial pathogens of animals, but this system has only been defined in relatively few genera. It was shown recently that S. meliloti uses heme as a nutritional iron source in Sinorhizobium meliloti and related species. The alpha-proteobacterial group to which S. meliloti belongs includes bacteria that form intracellular or close associations with higher eukaryotes in either a pathogenic or symbiotic context. Preliminary evidence suggests that genes involved in heme transport and metabolism in symbiotic S. meliloti have homologs in related animal pathogens. The broad objective of the proposed work is to characterize the heme utilization system in S. meliloti as an experimentally tractable model for the alpha-proteobacteria, and to identify common molecular themes in pathogenic and symbiotic interactions with higher eukaryotes. The ShmR protein is a putative heme receptor that was identified as an outer membrane protein that binds heme, and is expressed in an iron-dependent manner. Evidence indicates that shmR is transcriptionally controlled by a heretofore unidentified regulatory system. ShmR homologs are found in taxonomically-related pathogens. Two specific aims are proposed to address iron-dependent control of heme transport. 1) Identify the cis-acting element within the shmR promoter that mediates control by iron. 2) Identify the regulatory protein that mediates iron control of the shmR gene. Control of shmR by iron is not mediated by the two known regulators, Irr or Fur. Identification of the iron-responsive cis-acting element within the shmR promoter gives us the means to identify the cognate regulator protein. This research will be done primarily in Montevideo, Uruguay at the Instituto de Investigaciones Bioldgicas Clemente Estable in collaboration with Elena Fabiano as an extension of NIH grant R01GM067966. The gross national income per capita of Uruguay is $3,790 according to the World Bank classification system.