Characterization of two newly isolated bacteriophages PW2 and PW4 and derived endolysins with lysis activity against Bacillus cereus group strains.

Abstract

This study characterized two novel Siphoviridae phages, PW2 and PW4, that can infect 52% and 44% of the tested Bacillus cereus group isolates and display relatively high activity against four cereulide-producing isolates belonging to B. weihenstephanensis and B. paranthracis. The genome sequences of PW2 and PW4 are similar to six known phages infecting B. cereus group isolates, which can be classified into two conserved groups, with the PW2 genome harboring conserved coding sequences (CDSs) from both groups. Two phage-derived endolysins, LysPW2 and LysPW4, which are predicted to encode N-acetylmuramoyl-L-alanine amidase, and their enzymatically active domains (EADs), LysPW2-EAD and LysPW4-EAD, were heterologously expressed. Both LysPW2 and LysPW4, especially the former, show a much wider host range than the phages, albeit still limited to the B. cereus group for the tested bacteria. The optimal temperature and pH for LysPW2 ability is 37 °C and pH 8.0 and for LysPW4 is 50 °C and pH 9.0. Neither LysPW2-EAD nor LysPW4-EAD show any lytic activity against vegetative cells of the tested B. cereus group isolates but can inhibit germination in 66.3% and 65.7% of spores, respectively. In addition, both LysPW2-EAD and LysPW4-EAD exhibit spore-binding capabilities.