Characterization of LysB4, an endolysin from the Bacillus cereus-infecting bacteriophage B4

The endolysin from B. cereus phage B4, designated LysB4, was identified and characterized. In silico analysis revealed that this endolysin had the VanY domain at the N terminus as the catalytic domain, and the SH3_5 domain at the C terminus that appears to be the cell wall binding domain. Biochemical characterization of LysB4 enzymatic activity showed that it had optimal peptidoglycan hydrolase activity at pH 8.0-10.0 and 50°C. The lytic activity was dependent on divalent metal ions, especially Zn2+. The antimicrobial spectrum was relatively broad because LysB4 lysed Gram-positive bacteria such as B. cereus, Bacillus subtilis and Listeria monocytogenes and some Gram-negative bacteria when treated with EDTA. LC-MS analysis of the cell wall cleavage products showed that LysB4 was an L-alanoyl-D-glutamate endopeptidase, making LysB4 the first characterized endopeptidase of this type to target B. cereus.LysB4 is believed to be the first reported L-alanoyl-D-glutamate endopeptidase from B. cereus-infecting bacteriophages. The properties of LysB4 showed that this endolysin has strong lytic activity against a broad range of pathogenic bacteria, which makes LysB4 a good candidate as a biocontrol agent against B. cereus and other pathogenic bacteria.Bacillus cereus is a Gram-positive, spore-forming, rod-shape bacterium that grows well in aerobic and anaerobic environments [1]. It causes food poisoning by producing two different types of toxins: an emetic toxin and a diarrheal toxin [2]. Although the symptoms caused by B. cereus food poisoning are relatively mild, the incidence of the disease is gradually increasing, and it can develop into severe disease [3]. In addition, B. cereus can survive at a wide temperature range and form spores in harsh environments, especially during food processing; therefore, measures to control B. cereus effectively in the food industry are necessary [4,5].Recently, endolysins have been explored as promising antibacterial agents. Endolysins are