Genome analysis of the Clostridium difficile phage ΦCD6356, a temperate phage of the Siphoviridae family

The temperate phages ΦCD6356 and ΦCD6365 were isolated and characterised following mitomycin C induction of 43 Clostridium difficile strains. Both phages belong to the Siphoviridae family and have genome sizes of 37,664 bp for ΦCD6356 based on sequence data and approximately 50 kb for ΦCD6365 based on restriction analysis. Protein analysis revealed similar protein profiles and indicated posttranslational processing of the ΦCD6356 major capsid protein. The genome sequence of ΦCD6356 is substantially different from other previously reported phage sequences and a putative function could be assigned to only 21 out of 59 predicted open reading frames. However, the genome organisation closely resembles that of other members of the Siphoviridae family which infect low GC-content Gram-positive bacteria. The modular organisation, genome synteny, presence of cohesive ends and posttranslational processing of the capsid protein suggest ΦCD6356 is a member of the proposed Sfi21-like genera. To our knowledge, this report represents the first C. difficile phage of the Siphoviridae family to be sequenced.