Lytic activity assay of PlyBt33, PlyBt33-N, and PlyBt33-IC. (a), (b), (c), and (d). Filter papers were soaked in the crude extract suspended in 20 mM Tris-HCl (pH8.0) of PlyBt33 (a), PlyBt33-N (b), and PlyBt33-IC (c) from E. coli M15, and E. coli M15 containing pQE-30 (d), and placed onto the bacterial lawn of B. thuringiensis HD-73. (e) Lysis of viable cells using purified PlyBt33 and PlyBt33-N. Tests were performed in 20 mM Tris-HCl with a final protein concentration of 2 μM at 37°C. Crude extract of E. coli M15 containing pQE-30 was used as a control to treat B. thuringiensis strain HD-73.