Recombinant Phage-Borne Endolysin Production

The recombinant phage-borne endolysin was prepared according to the method described previously by Maciejewska et al. (2017) (link). Briefly, the coding sequence of Klebsiella phage KP27 endopeptidase was amplified using Pfu polymerase (Thermo Fisher Scientific, Waltham, MA, United States) and cloned into the commercially available pEXP-5-CT/TOPO^® TA expression vector (Invitrogen, Thermo Fisher Scientific, Waltham, MA, United States) according to the manufacturer recommendations. The expression was conducted for 18 h at 20°C using E. coli BL21 (DE3) pLysS (Agilent Technologies, Santa Clara, CA, United States) and isopropyl-β-D-1-thiogalactopyranoside (IPTG; the final concentration of 0.5 mmol/L) as an inductor of the expression. The recombinant protein was purified from the filtered supernatant by affinity chromatography using NGC medium pressure chromatography systems (Bio-Rad, Hercules, CA, United States) combined with 5-ml nickel columns using Bio-Scale Mini Profinity IMAC Cartridges (Bio-Rad, Hercules, CA, United States) and dialyzed against a PBS buffer. The concentration of purified recombinant enzyme was then determined fluorimetrically (Qubit^® Protein Assay Kit, Molecular Probes, Thermo Fisher Scientific, Waltham, MA, United States).