A Novel Acinetobacter Phage Cato: Lytic Myovirus Containing Tailspike Depolymerase

Acinetobacter baumannii is one of the most significant pathogens causing nosocomial infections. In this study, we present the characterization of novel virulent bacteriophage Cato, which specifically infects A. baumannii strains with a K102 capsular polysaccharide structure. The phage genome was annotated and analyzed. The phage shares similar genome organisation with the viruses belonging to the genus Obolenskvirus of the family Myoviridae. Linear double-stranded DNA genome of phage Cato is 45,188 bp-long, and contains 82 open reading frames. Putative functions were assigned for products of 27 predicted genes. The N-terminal domains of the tailspikes show a high level of homology, whereas the CPS-recognizing/degrading parts of the proteins are more versatile. HMM-HMM motif comparison and structural modelling of tailspike trimer (Fig. 4) confirm this complex structure. The tail fiber protein encoded in the Cato genome, can also participate in the attachment of the phage to A. baumannii bacterial surface. The gene encoding phage tailspike depolymerase was cloned, expressed, and purified. The recombinant depolymerase was found to be highly specific and formed opaque halos only on the bacterial lawn of the host bacterial strain.