Effect of heme vs. non-heme iron supplements on gut microbiome fitness

(1) Del Norte High School, San Diego, California, (2) Oak Valley Middle School, San Diego, California

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About 80% of people around the world suffer from iron deficiency, and doctors suggest taking over-the- counter supplements. However, dietary iron comes in two main forms: heme and non-heme. Both affect the carefully held balance of bacteria in our gut differently. This project studied the influence of heme and non-heme iron on the growth of pathogenic Serratia marcescens and non-pathogenic Escherichia coli bacteria. We hypothesized that the growth of bacteria would increase as the iron concentration rose, with the influence of heme iron being stronger than that of non-heme iron, as numerous previous studies have found that heme iron is more readily absorbed. In the growth medium, we grew E. coli and S. marcescens separately in no-iron control plates, increasing concentrations of heme or non-heme iron, or 0.5 μg/mL Ciprofloxacin, an antibiotic that kills bacteria. Then, we grew the bacteria together in a moderate concentration of non-heme or heme iron to test species competition. The results largely confirmed the hypothesis. In higher iron concentrations, both heme and non-heme iron elevated bacterial growth, suggesting that a greater quantity of free iron promotes bacterial growth. However, in the highest iron concentration of heme or non-heme iron, bacterial growth decreased, as overabsorption caused cytotoxicity. Heme iron plates had a higher bacterial growth than non-heme iron plates likely due to better iron absorption. The large magnitude by which the growth of S. marcescens was increased by heme iron in comparison to E. coli demonstrates the potential dangers of overconsumption of heme iron and suggests that some pathogenic bacteria can conduct iron absorption more efficiently. As ingesting too much iron can lead to dysbiosis and intestinal diseases, the conclusion of this study makes an important contribution to the relative safeties of heme and non-heme iron consumption.

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