Requirement of Staphylococcus aureus ATP-Binding Cassette-ATPase FhuC for Iron-Restricted Growth and Evidence that It Functions with More than One Iron Transporter

Abstract

In Staphylococcus aureus, fhuCBG encodes an ATP-binding cassette (ABC) transporter that is required for the transport of iron(III)-hydroxamates; mutation of either fhuB or fhuG eliminates transport. In this paper, we describe construction and characterization of an S. aureus fhuCBG deletion strain. The ⌬fhuCBG::ermC mutation not only resulted in a strain that was incapable of growth on iron(III)-hydroxamates as a sole source of iron but also resulted in a strain which had a profound growth defect in iron-restricted laboratory media. The growth defect was not a result of the inability to transport iron(III)-hydroxamates since S. aureus fhuG::Tn917 and S. aureus fhuD1::Km fhuD2::Tet mutants, which are also unable to transport iron(III)-hydroxamates, do not have similar iron-restricted growth defects. Complementation experiments demonstrated that the growth defect of the ⌬fhuCBG::ermC mutant was the result of the inability to express FhuC and that this was the result of an inability to transport iron complexed to the S. aureus siderophore staphylobactin. Iron is an essential micronutrient for virtually all microorganisms owing to its wide range of redox potentials. Either alone or incorporated into heme or iron-sulfur clusters, iron serves as the catalytic center of enzymes involved in critical cellular processes such as DNA synthesis and electron transport. However, despite the fact that iron is plentiful on Earth, the amount of free iron in biological systems is low due to its tendency to form insoluble oxyhydroxides under aerobic conditions at a neutral pH. The amount of iron available in the host environment is further reduced by sequestration into proteins such as transferrin and lactoferrin; virtually no free iron exists in living organisms (7). Transport of iron(III)-staphylobactin is dependent uponIn order to overcome iron limitation, most successful pathogens employ several strategies to acquire the quantities of iron necessary to cause infection (49). One such strategy is production of low-molecular-weight iron-chelating molecules termed siderophores which, together with their cognate cell surface binding proteins and transporters, provide an efficient system for iron acquisition (for a recent review, see reference 25). Indeed, there is considerable evidence demonstrating the importance of siderophore-mediated iron acquisition systems for the virulence of many disease-causing bacteria, including gram-negative bacteria such as Escherichia coli (50) and Yersinia enterocolitica (22) and gram-positive bacteria such as Staphylococcus aureus (14) and Bacillus anthracis (9).S. aureus is an important human pathogen in both community and hospital settings; it is a leading cause of nosocomially acquired infection. This organism is capable of causing infections ranging from minor (e.g., impetigo and food poisoning) to more severe (e.g., bacteremia, necrotizing pneumonia, endocarditis, and osteomyelitis) (13). Moreover, S. aureus is a major threat to the health care system since it is becoming increasingly resistant ...

Staphylococcus aureus Transporters Hts, Sir, and Sst Capture Iron Liberated from Human Transferrin by Staphyloferrin A, Staphyloferrin B, and Catecholamine Stress Hormones, Respectively, and Contribute to Virulence

“…Where siderophore production continues in the absence of transport, the growth medium represents a more chelated environment to the bacteria. To begin to assess this for S. aureus, we observed that when strains were grown in unchelated TMS broth (i.e., no exogenous chelator added), growth defects were noted for mutants lacking both staphyloferrin transporters (sir hts) or the ATPase required to energize both transporters (fhuC) (3,62). This growth defect was not apparent for a mutant unable to produce staphyloferrins (sbn sfa) (Fig.…”

The Suf Iron-Sulfur Cluster Biosynthetic System Is Essential in Staphylococcus aureus, and Decreased Suf Function Results in Global Metabolic Defects and Reduced Survival in Human Neutrophils

“…Growth of the WT, sufD*, and sufD* suf ϩ strains was monitored in the presence of 2,2-dipyridyl (DIP), which is a cell-permeable divalent metal chelator with specificity for Fe (47). An fhuC::Tn mutant that is defective in Fe scavenging was included as an experimental control (48). The sufD* and fhuC::Tn strains displayed decreased growth compared to the WT when cultured in the presence of DIP, and the phenotype of the sufD* mutation could be genetically complemented (Fig.…”

Heme Coordination by Staphylococcus aureus IsdE

“…Construction of S. aureus isdE::K m -Allelic replacement, using methodologies described previously (38), was used to generate a non-polar insertion mutation in the chromosomal copy of isdE; the kanamycin cassette, from plasmid pDG782 (39), was inserted into a unique EcoRI site present within the isdE coding region. The Newman isdE mutant was named strain H834.…”