Amino acid sequence alignment and structural composition of the studied Bacillus endolysins. (a) Alignment of the amino acid sequences of PlyBt33 with other bacteriophage endolysins. PlyPH, PlyBa04, and PlyL were the putative B. anthracis prophage endolysins [9, 16, 22]; PlyG was the endolysin from B. anthracis phage Gamma [17, 28]; Ply21 was the endolysin from B. cereus phage TP21[9, 29]. Residues critical for the cell wall binding activity of PlyG to B. anthracis and the corresponding residues in the other endolysins were boxed in red. (b) Schematic representation of PlyBt33 and other Bacillus. sp. endolysins. Amidase_2 and GH-25 represented the catalytic region of each endolysin; Amidase02_C and SH3_5 represented the cell wall binding region of each endolysin. The numbers above the rectangles corresponded to amino acid residue positions.