The Bordetella bhu Locus Is Required for Heme Iron Utilization

Abstract

Bordetella pertussis and Bordetella bronchiseptica are capable of obtaining iron from hemin and hemoglobin. Genes encoding a putative bacterial heme iron acquisition system (bhu, for Bordetella heme utilization) were identified in a B. pertussis genomic sequence database, and the corresponding DNA was isolated from a virulent strain of B. pertussis. A B. pertussis bhuR mutant, predicted to lack the heme outer membrane receptor, was generated by allelic exchange. In contrast to the wild-type strain, bhuR mutant PM5 was incapable of acquiring iron from hemin and hemoglobin; genetic complementation of PM5 with the cloned bhuRSTUV genes restored heme utilization to wild-type levels. In parallel studies, B. bronchiseptica bhu sequences were also identified and a B. bronchiseptica bhuR mutant was constructed and confirmed to be defective in heme iron acquisition. The wild-type B. bronchiseptica parent strain grown under low-iron conditions produced the presumptive BhuR protein, which was absent in the bhuR mutant. Furthermore, production of BhuR by iron-starved B. bronchiseptica was markedly enhanced by culture in hemin-supplemented medium, suggesting that these organisms sense and respond to heme in the environment. Analysis of the genetic region upstream of the bhu cluster identified open reading frames predicted to encode homologs of the Escherichia coli ferric citrate uptake regulators FecI and FecR. These putative Bordetella regulators may mediate heme-responsive positive transcriptional control of the bhu genes.

Norepinephrine Mediates Acquisition of Transferrin-Iron in Bordetella bronchiseptica

“…Experimental cultures consisted of iron-depleted SS medium containing 200 g/ml partially iron-saturated transferrin supplemented with either 50 M norepinephrine or 50 M norepinephrine and 36 M FeSO 4 . Each culture additionally contained 1.67 Ci/ml of [ for 55 Fe. The means of triplicate determinations Ϯ 1 standard deviation are reported and representative of two experiments.…”

“…bronchiseptica strains were grown in iron-replete SS medium for 24 h followed by growth for 16 h in iron-depleted SS medium. Bacteria were harvested by centrifugation and subcultured to parallel iron-depleted SS cultures containing 200 g/ml 55 Fe-transferrin at an initial optical density (600 nm) of 0.2. One set of parallel cultures was additionally supplemented with either 50 M norepinephrine or 50 M norepinephrine and 36 M FeSO 4 .…”

“…The respiratory pathogens Bordetella bronchiseptica and Bordetella pertussis have multiple characterized mechanisms of iron acquisition, including transport of heme-iron (55), biosynthesis and utilization of the alcaligin siderophore (10,27), and uptake of catechol xenosiderophores, such as enterobactin (4,8). In addition, there are other putative outer membrane iron transporters encoded in the Bordetella genome for which the ligand is unknown (41).…”

Transcriptional organization, regulation and role of the Porphyromonas gingivalis W83 hmu haemin-uptake locus

“…Since haemin is too large to freely diffuse through the bacterial membranes, bacteria have also developed mechanisms to transport the haemin across the membrane(s). Several reports show that the genes encoding the haemin-uptake systems are organized in operons (Ochsner et al, 2000;Stojiljkovic & Hantke, 1994;Thompson et al, 1999;Vanderpool & Armstrong, 2001;Wyckoff et al, 1998), indicating that such organization of these uptake systems is a common theme.…”

Resistance ofNeisseria meningitidisto the Toxic Effects of Heme Iron and Other Hydrophobic Agents Requires Expression ofght

“…It has been established that iron contained in heme can serve as the source of iron in a wide range of bacteria. Heme also performs a crucial role in many metabolic processes within the cell (20,29,33,35). However, the internal presence of heme, or excess iron resulting from its degradation, can have detrimental effects because heme can also facilitate oxidative damage within the bacteria.…”