Synthetic Gut Bead Model for Microbiome

mucin-alginate beads were used for small intestinal simulations and prepared by dripping a 5×-boiled mucin-alginate solution [50 g L⁻¹ mucin (Carl Roth), 12 g L⁻¹ agar (VWR), 12 g L⁻¹ alginate (Carl Roth) and 2.22 ml L⁻¹ 10 M NaOH (Chem-Lab)] into crosslinking solution containing 7.6 g L⁻¹ CaCl₂.2H₂O (VWR). This approach was implemented as the small alginate beads allowed for sterile sampling of colonized beads and addition of fresh beads via a 50 ml-syringe with catheter tip (Novolab) connected to an inlet port. Sterility of such handlings was a prerequisite as one worked with a synthetic consortium in multiple ileal simulations. In contrast, for the colonic microbiota, the conventional approach using mucin-covered microcosms was used as previously described by Van den Abbeele et al. (2012) (link). A buffer comprising (g L⁻¹) K₂HPO₄ (8.8; Chem-Lab) and KH₂PO₄ (6.8; Chem-Lab) was used to rinse luminal content from mucosal samples. Half of the mucus-alginate beads and mucin-covered microcosms were replaced every 2 days.