P712 is a temperate phage, which belongs to the P335 group of Siphoviridae phages, infecting the dairy starter bacterium Lactococcus lactis. The lytic cassette of this phage encodes a putative membrane protein, ORF54, of unknown function, a predicted (anti-)pinholin HOLTP712 and the LysTP712 endolysin which possesses an N-terminal lysozyme GH_25 catalytic domain and two LysM motifs in the cell wall binding (CBD) domain. holTP712 features a dual start motif and two holin proteins are synthesized when the gene is overexpressed from a plasmid. After induction of TP712 lysogens with MitC, lysis can be triggered by ionophores suggesting a pinholin mode of action similar to that of E. coli phage 21. LysTP712 appears to be a secreted endolysin with a regular signal peptide which must be removed upon export, otherwise pre-LysTP712 is inactive in zymograms. Extra protein bands are detected during purification of C-terminally His-tagged LysTP712. These are likely the result of proteolytic degradation rather than extra CBDs, typical of a multimeric endolysin, which are translated from an intragenic translational initiation start site. Expression of the three genes or only the holin-endolysin pair under the control of an inducible promoter is not sufficient to promote lysis from within in L. lactis. Interestingly, zymograms of whole protein extracts from MitC induced lysogens revealed two lytic bands, corresponding to the mature LysTP712 and an additional band of approximately 27 kDa. Whether this peptidoglycan hydrolase is encoded by the phage itself or is provided by the host is currently under investigation.

Trabajo presentado en la conference Viruses of Microbes, celebrada en Liverpool (Reino Unido) del 18 al 22 de julio de 2016

Peer reviewed