Bacterial strains and culture conditions

Escherichia coli DH5α and E. coli MC1022 were cultured in LB broth (10 g/L NaCl, 10 g/L tryptone, and 5 g/L yeast extract, pH 7.0) at 37°C with shaking. B. catenulatum #27, which was previously isolated from human fecal samples in our lab and identified by 16S rRNA gene sequence analysis, was cultured in MRS (De Man, Rogosa, and Sharpe) broth at 37°C under anaerobic condition (Whitley A95 Anaerobic Workstation, Don Whitley Scientific, Bradford, UK). For antibiotic selection of recombinant strains, 100 μg/mL of ampicillin (Sigma, Poole, UK) was used for E. coli while 15 and 5 μg/mL of chloramphenicol (Sigma) were used for E. coli and B. catenulatum, respectively.