Heme iron sources
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Heme Iron Sources: Insights from Recent Research
Introduction to Heme Iron Sources
Heme iron, a type of iron found in hemoglobin and myoglobin, is a crucial nutrient for many organisms, including humans and various pathogens. It is known for its high bioavailability compared to non-heme iron. This article synthesizes recent research on the sources and utilization of heme iron, highlighting its significance in both dietary contexts and microbial iron acquisition systems.
Heme Iron in Pathogenic Bacteria
Neisseriae and the hemO Gene
Pathogenic bacteria such as Neisseria meningitidis and Neisseria gonorrhoeae utilize heme compounds as essential iron sources. The hemO gene plays a critical role in this process. It is necessary for the utilization of heme, hemoglobin, and haptoglobin-hemoglobin complexes. Mutants lacking the hemO gene cannot use heme sources, although they can still assimilate iron from transferrin and iron-citrate complexes. This gene is also linked to the expression of the HmbR hemoglobin receptor, indicating a broader regulatory role in heme utilization.
Serratia marcescens and HasA Protein
Serratia marcescens employs an extracellular heme-binding protein, HasA, to acquire heme from hemoglobin. This protein is secreted under iron-depleted conditions and is essential for heme acquisition, demonstrating a sophisticated mechanism for iron uptake independent of siderophore production.
Mycobacterium tuberculosis
Mycobacterium tuberculosis can utilize heme as an iron source, suggesting the presence of a yet-unknown heme acquisition system. This ability is crucial for its survival and pathogenicity within the iron-scarce environment of the human host.
Heme Iron in Non-Pathogenic Bacteria
Rhizobium meliloti
Non-pathogenic bacteria like Rhizobium meliloti can also utilize heme compounds as iron sources. This bacterium can use heme, hemoglobin, and leghemoglobin under iron-depleted conditions, sharing components with siderophore-mediated iron transport systems. This ability is significant for its symbiotic relationship with host plants.
Heme Iron in Dietary Sources
Plant-Based Heme Iron
Heme iron is not only found in animal products but also in plant sources, particularly in the root nodules of leguminous plants like soy. Studies using a Caco-2 cell culture model have shown that soy root nodule hemoglobin (LHb) can improve iron bioavailability, making it a potential novel food fortificant. This plant-based heme iron shows promise for enhancing dietary iron intake, especially in vegetarian and vegan diets.
Red Meat and Blood
Heme-containing proteins, abundant in red meat and blood, are highly bioavailable dietary iron sources. These proteins, including hemoglobin and myoglobin, have been extensively studied for their structures and bioactivity mechanisms. They are widely used in food fortification due to their high bioavailability and fewer side effects compared to non-heme iron supplements.
Heme Iron Utilization in Fungi
Candida albicans and Human Serum Albumin
Fungi, such as Candida albicans, utilize heme as a major iron source. Interestingly, human serum albumin (HSA), a heme-scavenging protein, facilitates rather than inhibits heme utilization by these fungi. This finding suggests that HSA can significantly impact heme-iron availability for pathogenic fungi, presenting a potential target for therapeutic interventions.
Conclusion
Heme iron is a vital nutrient with high bioavailability, essential for both human health and microbial survival. Pathogenic bacteria and fungi have evolved sophisticated mechanisms to acquire heme iron from their hosts, while non-pathogenic bacteria and plants also utilize heme iron effectively. Understanding these mechanisms and sources can inform dietary strategies and therapeutic approaches to manage iron deficiency and microbial infections.
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