Bacterial strains, plasmids, cell lines and growth conditions

The bacterial strains, cell lines, and plasmids used in this study are listed in Supplementary Table ^S2. E. coli was grown in Luria-Bertani broth, while L. monocytogenes EGDe was cultivated in BHI or MM⁵¹ at 37 °C or 24 °C. If appropriate, the media were supplemented with the following antibiotics: erythromycin (300 μg/ml for E. coli or 10 μg/ml for L. monocytogenes), kanamycin (50 µg/ml), and chloramphenicol (10 µg/ml). For solid media, 1.5% agar (w/v) was added. Human colon ECs (Caco-2 cells, ATCC HTB-37) and human larynx squamous cell carcinoma cells (HEp-2 cells, ATCC CCL-23) were received from the American Type Culture Collection and were cultured at 37 °C and 5% CO₂ in Dulbecco’s Modified Eagle Medium (Biochrom KG, Berlin, Germany) supplemented with 10% fetal calf serum (Pan Biotech, Aidenbach, Germany). For RNA isolation, 50.5 ml of BHI was inoculated with 0.5 ml of a L. monocytogenes overnight culture and incubated at 37 °C or 24 °C with shaking (150 rpm). Aerobic growth in broth was conducted in Erlenmeyer flasks with constant shaking; anaerobic growth was performed in sealed Falcon tubes. Growth was monitored by measuring OD₆₀₀ with a Lambda Bio + spectrophotometer (Perkin Elmer, Waltham, MA, USA). If appropriate, 3.5 ml of BHI supplemented with 10 mM 1,2-PD (Sigma-Aldrich, Taufkirchen, Germany) and/or 25 nm cobalamin (Applichem, Darmstadt, Germany) in a 15-ml glass tube was inoculated with 0.25 ml of an L. monocytogenes overnight culture and incubated at 37 °C with shaking.