Conservation and Loss of a Putative Iron Utilization Gene Cluster among Genotypes of Aspergillus flavus

Iron is an essential component for growth and development. Despite relative abundance in the environment, bioavailability of iron is limited due to oxidation by atmospheric oxygen into insoluble ferric iron. Filamentous fungi have developed diverse pathways to uptake and use iron. In the current study, a putative iron utilization gene cluster (IUC) in Aspergillus flavus was identified and characterized. Gene analyses indicate A. flavus may use reductive as well as siderophore-mediated iron uptake and utilization pathways. The ferroxidation and iron permeation process, in which iron transport depends on the coupling of these two activities, mediates the reductive pathway. The IUC identified in this work includes six genes and is located in a highly polymorphic region of the genome. Diversity among A. flavus genotypes is manifested in the structure of the IUC, which ranged from complete deletion to a region disabled by multiple indels. Molecular profiling of A. flavus populations suggests lineage-specific loss of IUC. The observed variation among A. flavus genotypes in iron utilization and the lineage-specific loss of the iron utilization genes in several A. flavus clonal lineages provide insight on evolution of iron acquisition and utilization within Aspergillus section Flavi. The potential divergence in capacity to acquire iron should be taken into account when selecting A. flavus active ingredients for biocontrol in niches where climate change may alter iron availability.

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Genes Essential to Iron Transport in the Cyanobacterium Synechocystis sp. Strain PCC 6803

Journal of Bacteriology ◽

10.1128/jb.183.9.2779-2784.2001 ◽

2001 ◽

Vol 183 (9) ◽

pp. 2779-2784 ◽

Cited By ~ 135

Author(s):

Hirokazu Katoh ◽

Natsu Hagino ◽

Arthur R. Grossman ◽

Teruo Ogawa

Keyword(s):

Iron Uptake ◽

Iron Transport ◽

Ferric Iron ◽

Iron Acquisition ◽

Complete Medium ◽

Iron Starvation ◽

Transporter Family ◽

Genes Encoding ◽

In Cells ◽

Pcc 6803

ABSTRACT Genes encoding polypeptides of an ATP binding cassette (ABC)-type ferric iron transporter that plays a major role in iron acquisition inSynechocystis sp. strain PCC 6803 were identified. These genes are slr1295, slr0513, slr0327, and recently reportedsll1878 (Katoh et al., J. Bacteriol. 182:6523–6524, 2000) and were designated futA1, futA2, futB, andfutC, respectively, for their involvement in ferric iron uptake. Inactivation of these genes individually or futA1and futA2 together greatly reduced the activity of ferric iron uptake in cells grown in complete medium or iron-deprived medium. All the fut genes are expressed in cells grown in complete medium, and expression was enhanced by iron starvation. ThefutA1 and futA2 genes appear to encode periplasmic proteins that play a redundant role in iron binding. The deduced products of futB and futC genes contain nucleotide-binding motifs and belong to the ABC transporter family of inner-membrane-bound and membrane-associated proteins, respectively. These results and sequence similarities among the four genes suggest that the Fut system is related to the Sfu/Fbp family of iron transporters. Inactivation of slr1392, a homologue offeoB in Escherichia coli, greatly reduced the activity of ferrous iron transport. This system is induced by intracellular low iron concentrations that are achieved in cells exposed to iron-free medium or in the fut-less mutants grown in complete medium.

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The fission yeast ferric reductase gene frp1+ is required for ferric iron uptake and encodes a protein that is homologous to the gp91-phox subunit of the human NADPH phagocyte oxidoreductase

Molecular and Cellular Biology ◽

10.1128/mcb.13.7.4342-4350.1993 ◽

1993 ◽

Vol 13 (7) ◽

pp. 4342-4350

Author(s):

D G Roman ◽

A Dancis ◽

G J Anderson ◽

R D Klausner

Keyword(s):

Fission Yeast ◽

Iron Uptake ◽

Ferric Iron ◽

Reductase Activity ◽

Iron Acquisition ◽

Protein A ◽

Mutant Gene ◽

Predicted Amino Acid Sequence ◽

Mrna Levels ◽

Ferric Reductase

We have identified a cell surface ferric reductase activity in the fission yeast Schizosaccharomyces pombe. A mutant strain deficient in this activity was also deficient in ferric iron uptake, while ferrous iron uptake was not impaired. Therefore, reduction is a required step in cellular ferric iron acquisition. We have cloned frp1+, the wild-type allele of the mutant gene. frp1+ mRNA levels were repressed by iron addition to the growth medium. Fusion of 138 nucleotides of frp1+ promoter sequences to a reporter gene, the bacterial chloramphenicol acetyltransferase gene, conferred iron-dependent regulation upon the latter when introduced into S. pombe. The predicted amino acid sequence of the frp1+ gene exhibits hydrophobic regions compatible with transmembrane domains. It shows similarity to the Saccharomyces cerevisiae FRE1 gene product and the gp91-phox protein, a component of the human NADPH phagocyte oxidoreductase that is deficient in X-linked chronic granulomatous disease.

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Secreted Pyomelanin of Legionella pneumophila Promotes Bacterial Iron Uptake and Growth under Iron-Limiting Conditions

Infection and Immunity ◽

10.1128/iai.00858-13 ◽

2013 ◽

Vol 81 (11) ◽

pp. 4182-4191 ◽

Cited By ~ 33

Author(s):

Huaixin Zheng ◽

Christa H. Chatfield ◽

Mark R. Liles ◽

Nicholas P. Cianciotto

Keyword(s):

Legionella Pneumophila ◽

Ferrous Iron ◽

Iron Uptake ◽

Iron Transport ◽

Ferric Iron ◽

Iron Acquisition ◽

Ferric Hydroxide ◽

Supernatant Fraction ◽

Content Type ◽

Ferrous Iron Transport

ABSTRACTIron acquisition is critical to the growth and virulence ofLegionella pneumophila. Previously, we found thatL. pneumophilauses both a ferrisiderophore pathway and ferrous iron transport to obtain iron. We now report that two molecules secreted byL. pneumophila, homogentisic acid (HGA) and its polymerized variant (HGA-melanin, a pyomelanin), are able to directly mediate the reduction of various ferric iron salts. Furthermore, HGA, synthetic HGA-melanin, and HGA-melanin derived from bacterial supernatants enhanced the ability ofL. pneumophilaand other species ofLegionellato take up radiolabeled iron. Enhanced iron uptake was not observed with a ferrous iron transport mutant. Thus, HGA and HGA-melanin mediate ferric iron reduction, with the resulting ferrous iron being available to the bacterium for uptake. Upon further testing ofL. pneumophilaculture supernatants, we found that significant amounts of ferric and ferrous iron were associated with secreted HGA-melanin. Importantly, a pyomelanin-containing fraction obtained from a wild-type culture supernatant was able to stimulate the growth of iron-starved legionellae. That the corresponding supernatant fraction obtained from a nonpigmented mutant culture did not stimulate growth demonstrated that HGA-melanin is able to both promote iron uptake and enhance growth under iron-limiting conditions. Indicative of a complementary role in iron acquisition, HGA-melanin levels were inversely related to the levels of siderophore activity. Compatible with a role in the ecology and pathogenesis ofL. pneumophila, HGA and HGA-melanin were effective at reducing and releasing iron from both insoluble ferric hydroxide and the mammalian iron chelates ferritin and transferrin.

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The fission yeast ferric reductase gene frp1+ is required for ferric iron uptake and encodes a protein that is homologous to the gp91-phox subunit of the human NADPH phagocyte oxidoreductase.

Molecular and Cellular Biology ◽

10.1128/mcb.13.7.4342 ◽

1993 ◽

Vol 13 (7) ◽

pp. 4342-4350 ◽

Cited By ~ 84

Author(s):

D G Roman ◽

A Dancis ◽

G J Anderson ◽

R D Klausner

Keyword(s):

Fission Yeast ◽

Iron Uptake ◽

Ferric Iron ◽

Reductase Activity ◽

Iron Acquisition ◽

Protein A ◽

Mutant Gene ◽

Predicted Amino Acid Sequence ◽

Mrna Levels ◽

Ferric Reductase

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Gene cluster for ferric iron uptake in Agrobacterium tumefaciens MAFF301001

Genes & Genetic Systems ◽

10.1266/ggs.77.137 ◽

2002 ◽

Vol 77 (3) ◽

pp. 137-137 ◽

Cited By ~ 7

Author(s):

Hiroyuki Sonoda ◽

Katsunori Suzuki ◽

Kazuo Yoshida

Keyword(s):

Agrobacterium Tumefaciens ◽

Gene Cluster ◽

Iron Uptake ◽

Ferric Iron

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Iron Pathways and Iron Chelation Approaches in Viral, Microbial, and Fungal Infections

Pharmaceuticals ◽

10.3390/ph13100275 ◽

2020 ◽

Vol 13 (10) ◽

pp. 275

Author(s):

Ravneet Chhabra ◽

Aishwarya Saha ◽

Ashkon Chamani ◽

Nicole Schneider ◽

Riya Shah ◽

...

Keyword(s):

Iron Uptake ◽

Fungal Infections ◽

Iron Acquisition ◽

Iron Chelation ◽

Essential Element ◽

Iron Availability ◽

Tight Control ◽

Potential Clinical Benefit ◽

Bacteria And Fungi ◽

Spread Of Infection

Iron is an essential element required to support the health of organisms. This element is critical for regulating the activities of cellular enzymes including those involved in cellular metabolism and DNA replication. Mechanisms that underlie the tight control of iron levels are crucial in mediating the interaction between microorganisms and their host and hence, the spread of infection. Microorganisms including viruses, bacteria, and fungi have differing iron acquisition/utilization mechanisms to support their ability to acquire/use iron (e.g., from free iron and heme). These pathways of iron uptake are associated with promoting their growth and virulence and consequently, their pathogenicity. Thus, controlling microorganismal survival by limiting iron availability may prove feasible through the use of agents targeting their iron uptake pathways and/or use of iron chelators as a means to hinder development of infections. This review will serve to assimilate findings regarding iron and the pathogenicity of specific microorganisms, and furthermore, find whether treating infections mediated by such organisms via iron chelation approaches may have potential clinical benefit.

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Identification of TbpA Residues Required for Transferrin-Iron Utilization by Neisseria gonorrhoeae

Infection and Immunity ◽

10.1128/iai.00020-08 ◽

2008 ◽

Vol 76 (5) ◽

pp. 1960-1969 ◽

Cited By ~ 20

Author(s):

Jennifer M. Noto ◽

Cynthia Nau Cornelissen

Keyword(s):

Neisseria Gonorrhoeae ◽

Iron Uptake ◽

Binding Proteins ◽

Iron Acquisition ◽

Uptake System ◽

Wild Type ◽

Conserved Motif ◽

Alanine Substitution ◽

Transferrin Binding Proteins ◽

Iron Utilization

ABSTRACT Neisseria gonorrhoeae requires iron for survival in the human host and therefore expresses high-affinity receptors for iron acquisition from host iron-binding proteins. The gonococcal transferrin-iron uptake system is composed of two transferrin binding proteins, TbpA and TbpB. TbpA is a TonB-dependent, outer membrane transporter critical for iron acquisition, while TbpB is a surface-exposed lipoprotein that increases the efficiency of iron uptake. The precise mechanism by which TbpA mediates iron acquisition has not been elucidated; however, the process is distinct from those of characterized siderophore transporters. Similar to these TonB-dependent transporters, TbpA is proposed to have two distinct domains, a β-barrel and a plug domain. We hypothesize that the TbpA plug coordinates iron and therefore potentially functions in multiple steps of transferrin-mediated iron acquisition. To test this hypothesis, we targeted a conserved motif within the TbpA plug domain and generated single, double, and triple alanine substitution mutants. Mutagenized TbpAs were expressed on the gonococcal cell surface and maintained wild-type transferrin binding affinity. Single alanine substitution mutants internalized iron at wild-type levels, while the double and triple mutants showed a significant decrease in iron uptake. Moreover, the triple alanine substitution mutant was unable to grow on transferrin as a sole iron source; however, expression of TbpB compensated for this defect. These data indicate that the conserved motif between residues 120 and 122 of the TbpA plug domain is critical for transferrin-iron utilization, suggesting that this region plays a role in iron acquisition that is shared by both TbpA and TbpB.

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Conserved Regions of Gonococcal TbpB Are Critical for Surface Exposure and Transferrin Iron Utilization

Infection and Immunity ◽

10.1128/iai.00280-13 ◽

2013 ◽

Vol 81 (9) ◽

pp. 3442-3450 ◽

Cited By ~ 14

Author(s):

Karen L. Ostberg ◽

Amanda J. DeRocco ◽

Shreni D. Mistry ◽

Mary Kathryne Dickinson ◽

Cynthia Nau Cornelissen

Keyword(s):

Iron Uptake ◽

Cell Envelope ◽

Iron Acquisition ◽

Site Directed Mutagenesis ◽

Uptake System ◽

Content Type ◽

Functional Roles ◽

Conserved Regions ◽

Transferrin Binding Proteins ◽

Iron Utilization

ABSTRACTThe transferrin-binding proteins TbpA and TbpB enableNeisseria gonorrhoeaeto obtain iron from human transferrin. The lipoprotein TbpB facilitates, but is not strictly required for, TbpA-mediated iron acquisition. The goal of the current study was to determine the contribution of two conserved regions within TbpB to the function of this protein. Using site-directed mutagenesis, the first mutation we constructed replaced the lipobox (LSAC) of TbpB with a signal I peptidase cleavage site (LAAA), while the second mutation deleted a conserved stretch of glycine residues immediately downstream of the lipobox. We then evaluated the resulting mutants for effects on TbpB expression, surface exposure, and transferrin iron utilization. Western blot analysis and palmitate labeling indicated that the lipobox, but not the glycine-rich motif, is required for lipidation of TbpB and tethering to the outer membrane. TbpB was released into the supernatant by the mutant that produces TbpB LSAC. Neither mutation disrupted the transport of TbpB across the bacterial cell envelope. When these mutant TbpB proteins were produced in a strain expressing a form of TbpA that requires TbpB for iron acquisition, growth on transferrin was either abrogated or dramatically diminished. We conclude that surface tethering of TbpB is required for optimal performance of the transferrin iron acquisition system, while the presence of the polyglycine stretch near the amino terminus of TbpB contributes significantly to transferrin iron transport function. Overall, these results provide important insights into the functional roles of two conserved motifs of TbpB, enhancing our understanding of this critical iron uptake system.

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Siderophore-Mediated Iron Acquisition Enhances Resistance to Oxidative and Aromatic Compound Stress inCupriavidus necatorJMP134

Applied and Environmental Microbiology ◽

10.1128/aem.01938-18 ◽

2018 ◽

Vol 85 (1) ◽

Cited By ~ 5

Author(s):

Changfu Li ◽

Lingfang Zhu ◽

Damin Pan ◽

Shuyu Li ◽

He Xiao ◽

...

Keyword(s):

Gene Cluster ◽

Aromatic Compound ◽

Stress Resistance ◽

Biofilm Formation ◽

Iron Uptake ◽

Iron Acquisition ◽

Acquisition System ◽

Content Type ◽

Swimming Motility ◽

Iron Acquisition System

ABSTRACTMany bacteria secrete siderophores to enhance iron uptake under iron-restricted conditions. In this study, we found thatCupriavidus necatorJMP134, a well-known aromatic pollutant-degrading bacterium, produces an unknown carboxylate-type siderophore named cupriabactin to overcome iron limitation. Using genome mining, targeted mutagenesis, and biochemical analysis, we discovered an operon containing six open reading frames (cubA–F) in theC. necatorJMP134 genome that encodes proteins required for the biosynthesis and uptake of cupriabactin. As the dominant siderophore ofC. necatorJMP134, cupriabactin promotes the growth ofC. necatorJMP134 under iron-limited conditions via enhanced ferric iron uptake. Furthermore, we demonstrated that the iron concentration-dependent expression of thecuboperon is mediated by the ferric uptake regulator (Fur). Physiological analyses revealed that the cupriabactin-mediated iron acquisition system influences swimming motility, biofilm formation, and resistance to oxidative and aromatic compound stress inC. necatorJMP134. In conclusion, we identified a carboxylate-type siderophore named cupriabactin, which plays important roles in iron scavenging, bacterial motility, biofilm formation, and stress resistance.IMPORTANCESince siderophores have been widely exploited for agricultural, environmental, and medical applications, the identification and characterization of new siderophores from different habitats and organisms will have great beneficial applications. Here, we identified a novel siderophore-producing gene cluster inC. necatorJMP134. This gene cluster produces a previously unknown carboxylate siderophore, cupriabactin. Physiological analyses revealed that the cupriabactin-mediated iron acquisition system influences swimming motility, biofilm formation, and oxidative stress resistance. Most notably, this system also plays important roles in increasing the resistance ofC. necatorJMP134 to stress caused by aromatic compounds, which provide a promising strategy to engineer more efficient approaches to degrade aromatic pollutants.

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Characterization of a Novel Iron Acquisition Activity That Coordinates the Iron Response with Population Density under Iron-Replete Conditions in Bacillus subtilis

Journal of Bacteriology ◽

10.1128/jb.00487-16 ◽

2016 ◽

Vol 199 (1) ◽

Cited By ~ 3

Author(s):

Emily M. Roy ◽

Kevin L. Griffith

Keyword(s):

Bacillus Subtilis ◽

Population Density ◽

Iron Uptake ◽

Ferric Iron ◽

Iron Acquisition ◽

Biological Processes ◽

Aerobic Growth ◽

Content Type ◽

E Coli

ABSTRACT Iron is an essential micronutrient required for the viability of many organisms. Under oxidizing conditions, ferric iron is highly insoluble (∼10−9 to 10−18 M), yet bacteria typically require ∼10−6 M for survival. To overcome this disparity, many bacteria have adopted the use of extracellular iron-chelating siderophores coupled with specific iron-siderophore uptake systems. In the case of Bacillus subtilis, undomesticated strains produce the siderophore bacillibactin. However, many laboratory strains, e.g., JH642, have lost the ability to produce bacillibactin during the process of domestication. In this work, we identified a novel iron acquisition activity from strain JH642 that accumulates in the growth medium and coordinates the iron response with population density. The molecule(s) responsible for this activity was named elemental Fe(II/III) (Efe) acquisition factor because efeUOB (ywbLMN) is required for its activity. Unlike most iron uptake molecules, including siderophores and iron reductases, Efe acquisition factor is present under iron-replete conditions and is regulated independently of Fur repressor. Restoring bacillibactin production in strain JH642 inhibits the activity of Efe acquisition factor, presumably by sequestering available iron. A similar iron acquisition activity is produced from a mutant of Escherichia coli unable to synthesize the siderophore enterobactin. Given the conservation of efeUOB and its regulation by catecholic siderophores in B. subtilis and E. coli, we speculate that Efe acquisition factor is utilized by many bacteria, serves as an alternative to Fur-mediated iron acquisition systems, and provides cells with biologically available iron that would normally be inaccessible during aerobic growth under iron-replete conditions. IMPORTANCE Iron is an essential micronutrient required for a variety of biological processes, yet ferric iron is highly insoluble during aerobic growth. In this work, we identified a novel iron acquisition activity that coordinates the iron response with population density in laboratory strains of Bacillus subtilis. We named the molecule(s) responsible for this activity elemental Fe(II/III) (Efe) acquisition factor after the efeUOB (ywbLMN) operon required for its uptake into cells. Unlike most iron uptake systems, Efe acquisition factor is present under iron-replete conditions and is regulated independently of Fur, the master regulator of the iron response. We speculate that Efe acquisition factor is highly conserved among bacteria and serves as a backup to Fur-mediated iron acquisition systems.

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