FIG. 5.

Lysis of cell walls of L. helveticus CNRZ 303 by the Mur-LH endolysin, measured by the decrease in absorbance at 600 nm. The cell walls were heated at 100°C for 1 h and then resuspended in a 25 mM Tris-HCl buffer (pH 8) to a final OD₆₀₀ of 1 (1.9 mg [dry weight]/ml). They were incubated at 40°C with the crude endolysin extract obtained from recombinant E. coli BL21/pET(lys) (▪) or with a crude nonrecombinant E. coli BL21/pET extract (□). A control was prepared without any extract added to the cell wall (•).