Iron Deficiency and Biofortification

Iron Deficiency

“According to the United Nations World Food Program, more than 870 million people are malnourished” [1]. Moreover, as the global population continues to increase to 9 billion in 2050, agricultural yields will need to increase by 70-100%;the World Health Organization (WHO) maintains that iron deficiency is one of the most common and widespread nutritional disorders in the world- “The numbers are staggering: 2 billion people – over 30% of the world’s population – are anemic, many due to iron deficiency” [2].

Iron is one of the most important nutrients for the human diet/body. It is an essential component of many enzymes critical for life. For instance, the protein, hemoglobin, that carries oxygen throughout the body, is dependent on iron.

Iron deficiency is the most common nutritional disorder in the world (2) and is prevalent in both developing and industrialized countries. Pregnant women, infants, and children need more iron, and are there are for more at risk for iron deficiency. 50% of anemia in the population of developing countries is attributed to iron deficiency. The World Health Organization estimates 1 out of every 2 preschool children and women in developing countries are iron deficient.

Iron deficiency anemia can occur during pregnancy, which increases the risk of health complications for small or premature babies causing them to die in the first year of their life. Iron deficiency in children and adolescence impairs mental development and learning capacity. For adults, Iron deficiency reduces the ability to do physical labor, which is a problem for developing countries. Iron deficiency also decreases immune function. Iron deficiency anemia in developing countries is often aggravated by infections and infectious diseases.

The most common cause of iron deficiency in plant soil is high pH soil. The most common remedy is the addition of sulfur pellets which lower the pH making iron more bioavailable (10). This process is usually planned for at least a year in advance, and cost range from $17.70- $22.50 per acre. Farmers can also supplement their fertilizer with chelated iron; the most popular chelators being Fe-DTPA, Fe-EDDHA, and Fe-EDTA. (Walworth)

One way researchers are currently trying to solve this problem is with biofortification of iron in crops. Instead of the traditional method of genetic modification of the plants, our team has been working on engineering a system of microbes in the soil that will produce molecules that help plants acquire iron.

Iron Biofortification

Plants are limited in the amount of iron they can pick up from the soil because iron, despite being one of the most abundant elements on Earth, is mostly found in its insoluble ferric, Fe (III), form. Most organisms can directly uptake only Fe (II). To facilitate the transport of insoluble Fe (III) into the cells, both plants and microbes produce chemicals called phytosiderophores, which bind to Fe (III) and transform it into a soluble compound that can be transported into the cells. Plant siderophores, or phytosiderophores, are used by many plants to uptake iron. These compounds are much more able to re-enter the plant cells than other microbial siderophores.

The traditional method of increasing iron in plants involves genetically modifying the plants to increase their phytosiderophore production so they can pick up and bring in more iron from the environment. This is done by either amplifying the genes for phytosiderophore production that the plant already has, or by inserting the genes from another plant that is generally has higher iron content and therefore more efficient phytosiderophore genes.

In one study, iron uptake was increased in rice through the upregulation of the gene nicotianamine synthase (NAS), which is one of the genes of phytosiderophore production, and was then fed to anemic rice. The mice that consumed the modified rice recovered more rapidly from anemia than ones fed control rice [3]. In another study, corn was modified to overexpress the binding protein ferritin in order to increase the iron content in the corn. The corn seeds were then ground into a flour paste, which had a significantly higher level of total iron content than flour paste ground from control plants [4].

By attempting to increase the iron content in plants through modification of the rhizosphere, we are trying to shift the paradigm of engineering transgenic plants to engineering the microbial community around these plants. It is known that microbes already support plant health by increasing the bioavailability of nutrients, helping plants become resistant to disease, floods, and drought, facilitating root growth, and aiding in their defense against pathogens [1]. The efficacy of microbial phytosiderophores was proven in a study with iron-starved tomatoes (Radzki 2013). They were able to restore healthy iron levels in tomatoes by the direct application of Chryseobacterium C138 and with media containing just the microbially produced phytosiderophores. Granted, this study used iron-starved conditions, we still believe the use of microbial phytosiderophores is essential to iron uptake in normal plants.

We believe that microbes can be engineered to provide even more benefits to plants, and we hope that our project will make more people aware of the crucial role of the rhizosphere to plant health and nutrition. Ideally, this awareness will encourage further scientific research into the specific roles that each type of microbial organism plays and advocate for the systematic management of microbial soil ecologies.

Citations

1. [1] Reid, Ann and Greene, Shannon E. How Microbes Can Help Feed the World. American Academy of microbiology. December 2012. Retrieved from http://academy.asm.org/images/stories/ documents/FeedTheWorld.pdf

2. [2] World Health Organization. Micronutrient Deficiencies. WHO website, 2014. Retrieved from http://www.who.int/nutrition/topics/ida/en/

3. [3] Lee, Sichul and You-Sun, Kim. Activation of Rice nicotianamine synthase 2 (OsNAS2) Enhances Iron Availability for Biofortification. Molecules and Cells vol 33, March 2012, pages 269-275.

4. [4] Drakakaki, Georgia and Marcel, Sylvain. Endosperm-specific co-expression of recombinant soybean ferritin and Aspergillus phytase in maize results in significant increases in the levels of bioavailable iron. Plant Molecular Biology vol 59, 2005, pages 869-880.

5. http://www.medscape.com/viewarticle/580999_2

6. http://www.cdc.gov/nutrition/everyone/basics/vitamins/iron.html

7. http://www.harvestplus.org/content/iron

8. http://www.who.int/nutrition/topics/ida/en/

9. http://www.ncbi.nlm.nih.gov/pubmed/11943635

10. Cost of sulfur, ammonium sulfate vs. calcium sulfate Calcium Products incorporated. Retrieved on October15, 2014 from http://calciumproducts.com/ag-products/product-supercal-humic/item/183-sulfur-ammonium-sulfate-calcium-sulfate/183-sulfur-ammonium-sulfate-calcium-sulfate

11. Walworth, J. Recognizing and Treating Iron Deficiency in the Home Yard. Retrieved on October 15, 2014 from http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1415.pdf

12. Radzki, W., Mañero, F. G., Algar, E., García, J. L., García-Villaraco, A., & Solano, B. R. (2013). Bacterial siderophores efficiently provide iron to iron-starved tomato plants in hydroponics culture. Antonie van Leeuwenhoek, 104(3), 321-330.