For nisin variants produced by E. coli, antimicrobial activity tests were conducted as described (Baumann et al., 2017), using the same nisin-sensitive and NisP-expressing L. lactis indicator strain. Briefly, cell lysates produced from 1 ml bacterial culture were normalized by harvested cell density (OD600) using PBS buffer. Alternatively, peptide samples purified by immobilized metal ion affinity chromatography (IMAC) were used. Chloramphenicol at 400 μg/ml was used as antibacterial control compound.