Lactococcus lactis NZ9000 pNZ-RBSpylTSnisA(amber) pIL3EryBTC was grown in CDM medium (containing 5 μg/ml each chloramphenicol and erythromycin) to an OD600 of 0.4. Overexpression was induced with 10 ng/ml nisin and the medium was supplemented with 1-5 mM Nε-Boc-L-lysine (BocK) to grow for another 3 h. After harvesting, the supernatant was filtered, acidified, and finally purified by ion exchange chromatography using a 5 ml HiTrap SP-Sepharose (GE Healthcare) column. Fractions showing antimicrobial activity were pooled, desalted, and finally freeze-dried. For HPLC purification on an Agilent 1260 Infinity LC instrument, samples showing antimicrobial activity were desalted with a Sephadex G10 column (GE Healthcare) and applied to a C12 column (Phenomenex 250 × 4.5 mm, 4 μm, Proteo 90Å) as described earlier (Zhou et al., 2016b).