ABSTRACT
Hypermucoviscous (HV) strains of capsular types K1, K2 and K57 are the most virulent representatives of the Klebsiella pneumoniae species. Eight novel bacteriophages lytic for HV K. pneumoniae were isolated and characterized. Three bacteriophages, KpV41, KpV475, and KpV71 were found to have a lytic activity against mainly K. pneumoniae of capsular type K1. Two phages, KpV74, and KpV763 were lytic for K2 capsular type K. pneumoniae, and the phage KpV767 was specific to K57-type K. pneumoniae only. Two more phages, KpV766, and KpV48 had no capsular specificity. The phage genomes consist of a linear double-stranded DNA of 40,395-44,623bp including direct terminal repeats of 180-246 bp. The G + C contents are 52.3-54.2 % that is slightly lower than that of genomes of K. pneumoniae strains being used for phage propagation. According to the genome structures, sequence similarity and phylogenetic data, the phages are classified within the genus Kp32virus and Kp34virus of subfamily Autographivirinae, family Podoviridae. In the phage genomes, genes encoding proteins with putative motifs of polysaccharide depolymerase were identified. Depolymerase genes of phages KpV71 and KpV74 lytic for hypermucoviscous K. pneumoniae of K1 and K2 capsular type, respectively, were cloned and expressed in Escherichia coli, and the recombinant gene products were purified. The specificity and polysaccharide-degrading activity of the recombinant depolymerases were demonstrated.