Abstract:[Background] Staphylococcus aureus is a common zoonotic opportunistic pathogen. With the emergence of multidrug resistant strains, it is urgent to develop antimicrobial agents with different modes of action from antibiotics. [Objective] To isolate S. aureus phage and identify its functional lysin components as an effective specific antimicrobial agent. [Methods] The whole genome sequence of the phage was assembled and annotated for the mining of putative lysin encoding genes. Two putative lysin genes were respectively cloned into a prokaryotic expression vector. SDS-PAGE and Western blotting were employed to confirm the expression of the target proteins. We then verified the lytic activity by spotting the expression product on the host bacterial lawn. [Results] The isolated phage in this study could lyse its host bacterium and was named vB_Sau_P68. The phage genome was 139 409 bp with the GC content of 31.0% and encoded 220 open reading frames (ORFs). Under the transmission electron microscope, the phage appeared as an icosahedron with a contractile tail, which belonged to Myoviridae. Two putative lysin genes were annotated in the phage genome. ORF161 was predicted to encode lysin with a CHAP catalytic domain and ORF163 with a SH3_5 binding domain. The results of SDS-PAGE and Western blotting showed that Lys161 was expressed successfully and had lytic activity, while the expression of Lys163 was not be detected. The Lys161 sequence had no signal peptide or transmembrane region, and random coil was its major secondary structural element. [Conclusion] In this study, two lysin genes were cloned from a Staphylococcus aureus phage genome and expressed. The results suggested that the CHAP catalytic domain had lytic activity, while the SH3_5 binding domain was not expressed. The findings provide a theoretical basis for the exploration of the acting mechanism and application of lysin.
