A decrease in iron availability to human gut microbiome reduces the growth of potentially pathogenic gut bacteria: an in vitro colonic fermentation study

Iron-supplements are widely consumed; however most of the iron is not absorbed and enters the colon where potentially pathogenic bacteria can utilise it for growth. This study investigated the effect of iron availability on human gut microbial composition and function using an in vitro colonic fermentation model inoculated with faecal microbiota from healthy adult donors, as well as examining the effect of iron on the growth of individual gut bacteria. Batch fermenters were seeded with fresh faecal material and supplemented with the iron chelator, bathophenanthroline disulphonic acid (BPDS). Samples were analysed at regular intervals to assess impact on the gut bacterial communities. The growth of Escherichia coli and Salmonella Typhimurium was significantly impaired when cultured independently in iron-deficient media. In contrast, depletion of iron did not affect the growth of the beneficial species, Lactobacillus rhamnosus, when cultured independently. Analysis of the microbiome composition via 16S-based metataxonomics indicated that under conditions of iron chelation, the relative abundance decreased for several taxa, including a 10% decrease in Escherichia and a 15% decrease in Bifidobacterium. Metabolomics analysis using 1 HNMR indicated that the production of SCFAs was reduced under iron-limited conditions. These results support previous studies demonstrating the essentiality of iron for microbial growth and metabolism, but, in addition, they indicate that iron chelation changes the gut microbiota profile and influences human gut microbial homeostasis through both compositional and functional changes.