GO:0033215 reductive iron assimilation: Iron Uptake Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0033215 reductive iron assimilation is a biological process in which extracellular Fe3+ is reduced to Fe2+ by a cell surface reductase and then transported into the cell by iron uptake proteins.
• The pathway is best characterized in fungi, where it operates alongside siderophore-mediated iron acquisition and contributes to virulence in several pathogens.
• Key protein components include cell surface ferric reductases, multicopper ferroxidases, and high-affinity iron permeases that together form a reductive uptake system.
• Reductive iron assimilation is not universally essential for virulence: in Aspergillus fumigatus, siderophore biosynthesis but not reductive iron assimilation is required for full virulence, whereas in other fungi it contributes to disease.
• Environmental factors such as lactic acid and host phagocytosis can modulate expression of reductive iron assimilation genes.
• CRISPR-based knockout, point mutation, knock-in, and overexpression models enable causal dissection of reductive iron assimilation genes in fungal and other organisms.
Description
Reductive iron assimilation (GO:0033215) is a conserved biological process that enables cells to acquire iron from the environment by first reducing insoluble ferric iron (Fe3+) to soluble ferrous iron (Fe2+) at the cell surface and then transporting the reduced iron across the membrane. This mechanism is particularly well studied in fungi, where it complements siderophore-mediated iron uptake and is critical for iron homeostasis under iron-limited conditions. The pathway is defined by the coordinated action of a cell surface reductase, a ferroxidase, and a high-affinity iron permease complex. Researchers study reductive iron assimilation because iron is an essential micronutrient for nearly all organisms, and its acquisition is tightly linked to microbial pathogenesis, host-pathogen interactions, and environmental iron cycling. In fungal pathogens such as Lichtheimia corymbifera, Aspergillus fumigatus, and Botrytis cinerea, components of this pathway influence virulence, oxidative stress resistance, and developmental transitions. Beyond pathogenesis, reductive iron assimilation contributes to reductive biomining of pyrite by methanogens, highlighting its broader biogeochemical significance. The pathway is also relevant to human health because disruptions in iron acquisition and homeostasis are associated with infections and iron-related disorders. Understanding the molecular players and regulatory logic of reductive iron assimilation provides a foundation for developing antifungal strategies and for engineering iron acquisition in biotechnology.
reductive iron assimilation At A Glance
| GO ID | GO:0033215 |
|---|---|
| GO term | reductive iron assimilation |
| Ontology | biological_process |
| Synonym | iron assimilation by reduction and transport |
| Definition | A process in which iron is solubilized by reduction from Fe3+ to Fe2+ via a cell surface reductase and subsequent transport of the iron across the membrane by iron uptake proteins. |
| Major function | High-affinity iron uptake through reduction and transport of ferric iron |
| Key components | Cell surface ferric reductase, multicopper ferroxidase, high-affinity iron permease |
| Taxonomic scope | Characterized in fungi, methanogens, and other organisms |
| Related processes | Siderophore biosynthesis and transport, iron homeostasis, oxidative stress response |
What Is GO:0033215?
Reductive iron assimilation (GO:0033215) is defined as a process in which iron is solubilized by reduction from Fe3+ to Fe2+ via a cell surface reductase and subsequent transport of the iron across the membrane by iron uptake proteins. In other words, cells first convert extracellular ferric iron into the more soluble ferrous form using a reductase enzyme, and then import the reduced iron through dedicated transport proteins. This process is distinct from siderophore-mediated iron acquisition, although the two systems can operate in parallel and are often co-regulated.
Why Is reductive iron assimilation Important in Cell Biology?
Reductive iron assimilation is important because iron is essential for fundamental cellular processes, and its acquisition through this pathway influences microbial survival, virulence, and interactions with host organisms. In pathogenic fungi, the ability to acquire iron via reduction and transport contributes to disease development, and components of this pathway are being explored as potential antifungal targets. The pathway also plays a role in environmental iron cycling and reductive biomining, underscoring its broad biological and biotechnological relevance.
• Provides a high-affinity mechanism for iron uptake under iron-limited conditions.
• Contributes to virulence in fungal pathogens such as Lichtheimia corymbifera and Botrytis cinerea.
• Operates alongside siderophore-mediated iron acquisition to maintain iron homeostasis.
• Influences resistance to oxidative stress and developmental transitions in fungi.
• Is modulated by host factors such as lactic acid and phagocytosis.
• Plays a role in reductive biomining of pyrite by methanogens.
• Represents a potential target for antifungal drug development.
• Enables genetic dissection of iron acquisition using CRISPR-based models.
What Happens During reductive iron assimilation?
Reduction of ferric iron at the cell surface
In simple terms: The cell uses an enzyme on its surface to convert insoluble iron into a more usable form.
The first step of reductive iron assimilation involves cell surface ferric reductases that reduce extracellular Fe3+ to Fe2+. This reduction is essential because ferric iron is poorly soluble and cannot be efficiently transported into the cell. In fungi, this step is mediated by plasma membrane reductases, and expression of these enzymes is induced under iron limitation.
Oxidation by ferroxidase and transport by permease
In simple terms: After reduction, a ferroxidase and a permease work together to move iron into the cell.
Following reduction, Fe2+ is re-oxidized by a multicopper ferroxidase and then transported across the membrane by a high-affinity iron permease. This coupled ferroxidase-permease system is a hallmark of reductive iron assimilation in fungi. Defects in the ferroxidase component can alter virulence, as shown in Botrytis cinerea where mutations in the ferroxidase result in hypervirulence.
Coordination with siderophore-mediated iron acquisition
In simple terms: The reductive pathway works together with other iron uptake systems to keep iron levels balanced.
Reductive iron assimilation is not the only iron acquisition strategy in fungi; it functions alongside siderophore biosynthesis and uptake. Studies in Aspergillus fumigatus demonstrated that siderophore biosynthesis, but not reductive iron assimilation, is essential for virulence, indicating that the two systems have distinct roles. In other fungi, such as Lichtheimia corymbifera, reductive iron assimilation genes are expressed during phagocytosis, suggesting a role in host interaction.
Regulation by environmental and host factors
In simple terms: The pathway can be turned on or off depending on conditions like iron availability or the presence of host molecules.
Expression of reductive iron assimilation genes is responsive to iron availability and host-derived factors. Lactic acid, a metabolite present in host niches, influences iron assimilation by a fungal pathogen via the reductive uptake pathway. During phagocytosis of Lichtheimia corymbifera, expression patterns of reductive iron assimilation genes change, and these changes have functional consequences for the pathogen.
Role in virulence and development
In simple terms: In some fungi, this iron uptake pathway helps the organism cause disease and complete its life cycle.
Reductive iron assimilation contributes to virulence in several fungal pathogens, although its importance varies by species. In Nomuraea rileyi, siderophore biosynthesis but not reductive iron assimilation is essential for conidiation, dimorphism transition, oxidative stress resistance, and virulence. In Botrytis cinerea, defects in the ferroxidase of the reductive iron assimilation system lead to hypervirulence, revealing a complex relationship between iron uptake and pathogenicity.
Key Genes Involved in GO:0033215 reductive iron assimilation
The following genes and proteins are experimentally implicated in reductive iron assimilation and its regulation across fungi and other organisms.
| Gene | Major Role | Research Relevance |
|---|---|---|
| FRE1 | Cell surface ferric reductase | Reduces Fe3+ to Fe2+ in reductive iron assimilation |
| FRE2 | Cell surface ferric reductase | Paralogous reductase contributing to iron reduction |
| FET3 | Multicopper ferroxidase | Oxidizes Fe2+ for permease-mediated transport |
| FTR1 | High-affinity iron permease | Transports iron across the plasma membrane |
| SID1 | Siderophore biosynthesis | Non-reductive iron acquisition, distinct from GO:0033215 |
| SID2 | Siderophore biosynthesis | Required for virulence in Aspergillus fumigatus |
| SREA | GATA-type iron regulator | Regulates iron acquisition genes including reductive pathway |
| HAPX | CCAAT-binding regulator | Coordinates iron homeostasis and virulence |
| LaeA | Global regulator of secondary metabolism | Influences siderophore and iron acquisition gene expression |
| BcFET1 | Ferroxidase in Botrytis cinerea | Mutations cause hypervirulence |
| NrrSid1 | Siderophore biosynthesis in Nomuraea rileyi | Essential for development and virulence |
| LcFRE1 | Reductase in Lichtheimia corymbifera | Expressed during phagocytosis |
| LcFET3 | Ferroxidase in Lichtheimia corymbifera | Part of reductive iron assimilation |
| LcFTR1 | Permease in Lichtheimia corymbifera | Iron transport during host interaction |
| AfFRE1 | Reductase in Aspergillus fumigatus | Not essential for virulence |
| AfFET3 | Ferroxidase in Aspergillus fumigatus | Not essential for virulence |
| AfFTR1 | Permease in Aspergillus fumigatus | Not essential for virulence |
How Is reductive iron assimilation Regulated?
Reductive iron assimilation is regulated at the transcriptional level in response to iron availability and host-derived signals. In fungi, GATA-type transcription factors such as SREA and CCAAT-binding factors like HAPX coordinate the expression of iron acquisition genes, including those involved in reductive uptake. Environmental factors such as lactic acid can modulate the pathway, as shown in a fungal pathogen where lactic acid influences iron assimilation via the reductive uptake pathway. During phagocytosis, expression of reductive iron assimilation genes is dynamically regulated, with functional consequences for the pathogen. Additionally, global regulators such as LaeA can influence iron acquisition gene expression in the context of secondary metabolism and virulence.
reductive iron assimilation and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| LcFRE1 | Mucormycosis (Lichtheimia corymbifera) | Knockout in L. corymbifera; phagocytosis assay |
| BcFET1 | Plant pathogenesis (Botrytis cinerea) | Point mutation or knockout in B. cinerea; virulence test |
| AfSID2 | Invasive aspergillosis (Aspergillus fumigatus) | Knockout in A. fumigatus; murine infection model |
| NrrSid1 | Fungal development and virulence (Nomuraea rileyi) | Knockout in N. rileyi; oxidative stress assay |
| SREA | Iron homeostasis and virulence | Knockout in Aspergillus spp.; iron-limited growth |
Fungal infections and virulence
Reductive iron assimilation contributes to the virulence of several fungal pathogens. In Lichtheimia corymbifera, an emerging cause of mucormycosis, genes involved in reductive iron assimilation are expressed during phagocytosis, and this expression has functional consequences for the pathogen. In Botrytis cinerea, defects in the ferroxidase that participates in the reductive iron assimilation system result in hypervirulence, indicating a complex role in plant pathogenesis. However, in Aspergillus fumigatus, siderophore biosynthesis but not reductive iron assimilation is essential for virulence, highlighting species-specific differences.
Iron homeostasis and oxidative stress
Iron acquisition is tightly linked to oxidative stress resistance. In Nomuraea rileyi, siderophore biosynthesis but not reductive iron assimilation is essential for resistance to oxidative stress, suggesting that the reductive pathway may have distinct roles under stress conditions. Proper regulation of iron uptake is critical to avoid iron overload and oxidative damage, and the reductive pathway is part of a broader iron homeostasis network.
Environmental and biotechnological relevance
Beyond pathogenesis, reductive iron assimilation is relevant to environmental iron cycling. Methanogens can perform reductive biomining of pyrite, a process that involves reductive iron acquisition. This highlights the potential of reductive iron assimilation in biotechnological applications such as bioleaching and metal recovery.
From reductive iron assimilation-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Is a ferric reductase required for iron uptake? | Knockout of FRE1/FRE2 in fungal strain; growth assay under iron limitation |
| Does a ferroxidase mutation alter virulence? | Point mutation in FET3; plant or animal infection model |
| Can a tagged permease be used to track localization? | Knock-in of fluorescent tag at FTR1 locus; live-cell imaging |
| Does overexpression of reductive iron assimilation genes enhance iron uptake? | Overexpression of FET3-FTR1 in fungal strain; iron uptake assay |
| Which genes are co-regulated with reductive iron assimilation? | CRISPR library screening under iron-limited conditions |
| Does lactic acid modulate reductive iron assimilation? | Wild-type and mutant strains exposed to lactic acid; gene expression analysis |
How to Study the reductive iron assimilation Process
| Method | What It Measures | Typical Application |
|---|---|---|
| RNA-seq | Transcript levels of iron acquisition genes | Expression profiling under iron limitation |
| qRT-PCR | Relative expression of specific genes | Validation of reductive iron assimilation gene induction |
| Ferric reductase assay | Enzymatic reduction of Fe3+ to Fe2+ | Functional characterization of FRE genes |
| Iron uptake assay | Intracellular iron accumulation | Measuring transport activity of FTR1 |
| CRISPR knockout | Loss-of-function phenotype | Testing gene essentiality for iron acquisition |
| Fluorescence microscopy | Protein localization | Visualizing tagged permease or ferroxidase |
| Virulence assay | Pathogenicity in host model | Assessing role of reductive iron assimilation in infection |
| CRISPR library screening | Fitness under iron-limited conditions | Identifying novel iron acquisition genes |
Transcriptional profiling of iron acquisition genes
RNA-seq and qRT-PCR are used to measure expression of reductive iron assimilation genes under different iron conditions and during host interaction. For example, expression patterns of reductive iron assimilation genes in Lichtheimia corymbifera were analyzed during phagocytosis. Lactic acid treatment was shown to influence iron assimilation gene expression in a fungal pathogen.
Genetic perturbation and phenotypic assays
Knockout, point mutation, and overexpression strains are generated to test the function of reductive iron assimilation genes. Growth assays under iron-limited conditions, oxidative stress tests, and virulence models are used to assess phenotypic consequences. In Botrytis cinerea, ferroxidase mutants were tested for virulence and showed hypervirulence.
Biochemical and imaging approaches
Ferric reductase activity assays, iron uptake measurements, and fluorescence microscopy of tagged proteins are used to study the reductive iron assimilation machinery. Localization of permeases and ferroxidases can be visualized using fluorescent protein fusions.
CRISPR library screening and bioinformatics
Genome-wide CRISPR screens can identify genes required for growth under iron limitation, revealing new components of reductive iron assimilation. Bioinformatics analysis of co-expression networks and regulatory motifs helps identify transcription factors controlling the pathway.
How CRISPR Can Be Used to Study GO:0033215 reductive iron assimilation
Knockout
CRISPR knockout is used to delete genes encoding ferric reductases, ferroxidases, or permeases to test their requirement for reductive iron assimilation. For example, knockout of the ferroxidase in Botrytis cinerea revealed a role in virulence. In Aspergillus fumigatus, knockout of reductive iron assimilation genes showed they are not essential for virulence, unlike siderophore biosynthesis genes.
Point Mutation
CRISPR point mutation can introduce specific amino acid substitutions in catalytic residues of ferric reductases or ferroxidases to dissect their enzymatic function. This approach is useful for separating the reductive iron assimilation function from other roles of the protein.
Knock-in
Knock-in of fluorescent or epitope tags at endogenous loci enables real-time tracking of reductive iron assimilation proteins. Tagged permeases and ferroxidases can be used to study localization and dynamics during iron uptake.
Overexpression
CRISPR activation or overexpression constructs can drive high-level expression of reductive iron assimilation genes to test whether increased iron uptake enhances growth or virulence. Overexpression of FET3-FTR1 in fungi can increase iron acquisition under iron-limited conditions.
How EDITGENE Supports reductive iron assimilation Research
Researchers studying reductive iron assimilation-related genes often need to determine whether a candidate gene is causally involved in iron uptake, virulence, or stress responses. EDITGENE provides CRISPR-based cell model services to enable precise genetic perturbations in fungal and other organisms, supporting functional studies of GO:0033215 and its components.
Contact EDITGENE today to design your custom CRISPR model for reductive iron assimilation research.
Frequently Asked Questions About reductive iron assimilation
What is reductive iron assimilation?
Reductive iron assimilation (GO:0033215) is a process in which iron is solubilized by reduction from Fe3+ to Fe2+ via a cell surface reductase and subsequent transport of the iron across the membrane by iron uptake proteins.
What genes are involved in reductive iron assimilation?
Key genes include ferric reductases (e.g., FRE1, FRE2), ferroxidases (e.g., FET3), and iron permeases (e.g., FTR1).
Why is reductive iron assimilation important for fungal virulence?
In some fungal pathogens, reductive iron assimilation contributes to virulence, although its importance varies by species; for example, it is not essential in Aspergillus fumigatus but affects virulence in Botrytis cinerea.
How is reductive iron assimilation regulated?
It is regulated transcriptionally by iron availability and factors such as SREA and HAPX, and can be modulated by host metabolites like lactic acid.
What is the difference between reductive iron assimilation and siderophore-mediated iron uptake?
Reductive iron assimilation uses reduction and transport, while siderophore-mediated uptake relies on secreted siderophores; the two systems can operate in parallel.
Which organisms use reductive iron assimilation?
It is best characterized in fungi, but also occurs in methanogens and other organisms.
What methods are used to study reductive iron assimilation?
Common methods include RNA-seq, ferric reductase assays, iron uptake assays, CRISPR knockout, and virulence tests.
Can CRISPR be used to study reductive iron assimilation genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression are used to dissect gene function in this pathway.
What diseases are associated with reductive iron assimilation?
It is associated with fungal infections such as mucormycosis and plant pathogenesis, and with iron homeostasis disorders.
What is the GO ID for reductive iron assimilation?
The GO ID is GO:0033215.
Conclusion
Reductive iron assimilation (GO:0033215) is a fundamental biological process for iron acquisition, involving cell surface reduction of Fe3+ to Fe2+ and subsequent transport by dedicated uptake proteins. Its components are critical for iron homeostasis and contribute to virulence in several fungal pathogens, though with species-specific differences. Studying this pathway using CRISPR-based models and functional assays provides insights into microbial pathogenesis and potential antifungal targets. Continued research on reductive iron assimilation will advance our understanding of iron biology and its applications in medicine and biotechnology.
References
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- 2. Gomes-Gonçalves A et al.. 2025. Lactic Acid Influences Iron Assimilation by a Fungal Pathogen via the Iron Reductive Uptake Pathway.. Microbiologyopen 14(6):e70167 PMID: 41400135
- 3. Condon BJ et al.. 2014. Reductive iron assimilation and intracellular siderophores assist extracellular siderophore-driven iron homeostasis and virulence.. Mol Plant Microbe Interact 27(8):793-808 PMID: 24762221
- 4. Vasquez-Montaño E et al.. 2020. Defects in the Ferroxidase That Participates in the Reductive Iron Assimilation System Results in Hypervirulence in Botrytis Cinerea.. mBio 11(4) PMID: 32753496
- 5. Li Y et al.. 2016. Siderophore Biosynthesis but Not Reductive Iron Assimilation Is Essential for the Dimorphic Fungus Nomuraea rileyi Conidiation, Dimorphism Transition, Resistance to Oxidative Stress, Pigmented Microsclerotium Formation, and Virulence.. Front Microbiol 7:931 PMID: 27379061
- 6. Spietz RL et al.. 2022. Reductive biomining of pyrite by methanogens.. Trends Microbiol 30(11):1072-1083 PMID: 35624031
- 7. Schrettl M et al.. 2004. Siderophore biosynthesis but not reductive iron assimilation is essential for Aspergillus fumigatus virulence.. J Exp Med 200(9):1213-9 PMID: 15504822
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