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Ferric rhizoferrin uptake into Morganella morganii: characterization of genes involved in the uptake of a polyhydroxycarboxylate siderophore.

ABSTRACT: Iron uptake in Morganella morganii, mediated by the fungal siderophore rhizoferrin, was studied. A Mud1 insertion mutant devoid of growth on ferric rhizoferrin was complemented by a chromosomal DNA fragment of M. morganii that encoded an outer membrane protein and a periplasmic protein named RumA and RumB (for rhizoferrin uptake into Morganella spp.), respectively. rumA and rumB have the same transcription polarity and are probably cotranscribed from an iron-regulated promoter upstream of rumA. A predicted Fur regulatory sequence upstream of rumA was confirmed by the Fur titration assay. At the N terminus of RumA, a putative TonB box contains a proline residue that inactivates TonB-dependent receptors and colicins when introduced at the same position into TonB boxes of Escherichia coli. Analysis of a 10-kb sequence flanking rumA and rumB on both sides revealed seven additional open reading frames for which no role in ferric rhizoferrin uptake could be discerned. Thus, rumA and rumB, both essential for transport of this siderophore, form an isolated operon. Additional genes required for ferric rhizoferrin translocation across the cytoplasmic membrane must map at sites distinct from rumA and rumB. Transport studies revealed that both 55Fe3+ and [3H]ketorhizoferrin are incorporated by M. morganii, demonstrating that rhizoferrin serves as a true iron carrier.

SUBMITTER: Kuhn S

PROVIDER: S-EPMC177684 | biostudies-other | 1996 Jan

REPOSITORIES: biostudies-other

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Ferric rhizoferrin uptake into Morganella morganii: characterization of genes involved in the uptake of a polyhydroxycarboxylate siderophore.

Kühn S S Braun V V Köster W W

Journal of bacteriology 19960101 2

Iron uptake in Morganella morganii, mediated by the fungal siderophore rhizoferrin, was studied. A Mud1 insertion mutant devoid of growth on ferric rhizoferrin was complemented by a chromosomal DNA fragment of M. morganii that encoded an outer membrane protein and a periplasmic protein named RumA and RumB (for rhizoferrin uptake into Morganella spp.), respectively. rumA and rumB have the same transcription polarity and are probably cotranscribed from an iron-regulated promoter upstream of rumA. ...[more]

PMID: 8550472

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Project description:Iron is a highly reactive metal that participates in several processes in prokaryotic and eukaryotic cells. Hosts and pathogens compete for iron in the context of infection. Chromobacterium violaceum, an environmental Gram-negative bacterial pathogen, relies on siderophores to overcome iron limitation in the host. In this work, we studied the role of the ferric uptake regulator Fur in the physiology and virulence of C. violaceum A Δfur mutant strain showed decreased growth and fitness under regular in vitro growth conditions and presented high sensitivity to iron and oxidative stresses. Furthermore, the absence of fur caused derepression of siderophore production and reduction in swimming motility and biofilm formation. Consistent with these results, the C. violaceum Δfur mutant was highly attenuated for virulence and liver colonization in mice. In contrast, a manganese-selected spontaneous fur mutant showed only siderophore overproduction and sensitivity to oxidative stress, indicating that Fur remained partially functional in this strain. We found that mutations in genes related to siderophore biosynthesis and a putative CRISPR-Cas locus rescued the Δfur mutant growth defects, indicating that multiple Fur-regulated processes contribute to maintaining bacterial cell fitness. Overall, our data indicated that Fur is conditionally essential in C. violaceum mainly by protecting cells from iron overload and oxidative damage. The requirement of Fur for virulence highlights the importance of iron in the pathogenesis of C. violaceumIMPORTANCE Maintenance of iron homeostasis, i.e., avoiding both deficiency and toxicity of this metal, is vital to bacteria and their hosts. Iron sequestration by host proteins is a crucial strategy to combat bacterial infections. In bacteria, the ferric uptake regulator Fur coordinates the expression of several iron-related genes. Sometimes, Fur can also regulate several other processes. In this work, we performed an in-depth phenotypic characterization of fur mutants in the human opportunistic pathogen Chromobacterium violaceum We determined that fur is a conditionally essential gene necessary for proper growth under regular conditions and is fully required for survival under iron and oxidative stresses. Fur also controlled several virulence-associated traits, such as swimming motility, biofilm formation, and siderophore production. Consistent with these results, a C. violaceumfur null mutant showed attenuation of virulence. Therefore, our data established Fur as a major player required for C. violaceum to manage iron, including during infection in the host.

Dataset Information

Ferric rhizoferrin uptake into Morganella morganii: characterization of genes involved in the uptake of a polyhydroxycarboxylate siderophore.

Publications

Ferric rhizoferrin uptake into Morganella morganii: characterization of genes involved in the uptake of a polyhydroxycarboxylate siderophore.

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