2.2 | Starter culture and culture conditions
The model gut microbiota in this study was prepared from dehydrated bacterial cultures of Lactobacillus acidophilus, Lactobacillus delbrueckii subspecies bulgaricus, Lactobacillus casei, Lactobacillus rhamnosus, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium longum and Streptococcus salivarius subspeciesthermophilus . Some experiments used monocultures ofEscherichia coli BL21 or Bifidobacterium longum subspeciesinfantis 35624 (Bifantis™, Align). To establish working bacterial cultures, dehydrated bacteria were first reconstituted in sterile peptone water (Oxoid). A 1 mL aliquot of the reconstituted bacteria was then added to 9 mL of de Man Rogosa and Sharpe (MRS) medium (Oxoid) supplemented with 0.05 % w/v L-cysteine (Amresco). The starter culture was grown at 37 °C anaerobically until the optical density at 600 nm (OD600) reached ≥ 1.5 before being used in experiments.