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Front Microbiol. 2016 Jan 6;6:1481. doi: 10.3389/fmicb.2015.01481. eCollection 2015.

Microbial Metabolism Shifts Towards an Adverse Profile with Supplementary Iron in the TIM-2 In vitro Model of the Human Colon.

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Department of Laboratory Medicine - Translational Metabolic Laboratory, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center Nijmegen, Netherlands.
Radboud Institute for Molecular Life Sciences, Center for Molecular and Biomolecular Informatics, Radboud University Medical CenterNijmegen, Netherlands; Theoretical Biology and Bioinformatics, Utrecht UniversityUtrecht, Netherlands; Department of Marine Biology, Institute of Biology, Federal University of Rio de JaneiroRio de Janeiro, Brazil.
TNO Innovation for Life Zeist, Netherlands.
NIZO food research, Kernhemseweg Ede Netherlands.
Argonne National Laboratory, University of Chicago Lemont, IL, USA.
Illumina Inc., Chesterford Research ParkLittle Chesterford, UK; DNAdigest, Future Business CentreCambridge, UK.
Illumina Inc., Chesterford Research Park Little Chesterford, UK.


Oral iron administration in African children can increase the risk for infections. However, it remains unclear to what extent supplementary iron affects the intestinal microbiome. We here explored the impact of iron preparations on microbial growth and metabolism in the well-controlled TNO's in vitro model of the large intestine (TIM-2). The model was inoculated with a human microbiota, without supplementary iron, or with 50 or 250 μmol/L ferrous sulfate, 50 or 250 μmol/L ferric citrate, or 50 μmol/L hemin. High resolution responses of the microbiota were examined by 16S rDNA pyrosequencing, microarray analysis, and metagenomic sequencing. The metabolome was assessed by fatty acid quantification, gas chromatography-mass spectrometry (GC-MS), and (1)H-NMR spectroscopy. Cultured intestinal epithelial Caco-2 cells were used to assess fecal water toxicity. Microbiome analysis showed, among others, that supplementary iron induced decreased levels of Bifidobacteriaceae and Lactobacillaceae, while it caused higher levels of Roseburia and Prevotella. Metagenomic analyses showed an enrichment of microbial motility-chemotaxis systems, while the metabolome markedly changed from a saccharolytic to a proteolytic profile in response to iron. Branched chain fatty acids and ammonia levels increased significantly, in particular with ferrous sulfate. Importantly, the metabolite-containing effluent from iron-rich conditions showed increased cytotoxicity to Caco-2 cells. Our explorations indicate that in the absence of host influences, iron induces a more hostile environment characterized by a reduction of microbes that are generally beneficial, and increased levels of bacterial metabolites that can impair the barrier function of a cultured intestinal epithelial monolayer.


BCFA; SCFA; gut microbiome; in vitro fermentation; iron supplementation; metabolome; metagenome; toxicity

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