The K26 capsular polysaccharide from Acinetobacter baumannii KZ-1098: Structure and cleavage by a specific phage depolymerase

The KL26 gene cluster responsible for the synthesis of the K26 capsular polysaccharide (CPS) of Acinetobacter baumannii includes rmlBDAC genes for L-rhamnose (L-Rhap) synthesis, tle to generate 6-deoxy-L-talose (L-6dTalp) from L-Rhap, and a manC gene for D-mannose (D-Manp) that is rare in Acinetobacter CPS. K26 CPS material was isolated from A. baumannii isolate KZ-1098, and studied by sugar analysis, Smith degradation, and one and two-dimensional 1H and 13C NMR spectroscopy before and after O-deacetylation with aqueous ammonia. The following structure of the branched hexasaccharide repeating unit of the CPS was established: →2)−β−D−Manp−1→4−β−D−Glcp−1→3−α−L−6dTalp−1→3−β−D−GlcpNAc−( 1→                3                                                   4                ↑                                                  │                1                                                  Acα−L−Rhap−2←1−α−D−Glcp The structural depolymerase of phage vB_AbaP_APK26 cleaved selectively the β-GlcpNAc-(1 → 2)-α-Manp linkage in the K26 CPS formed by WzyK26 to give monomer, dimer, and trimer of the CPS repeating unit, which were characterized by high-resolution electrospray ionization mass spectrometry as well as 1H and 13C NMR spectroscopy. The wzyK26 gene responsible for this linkage and the manC gene were only found in six A. baumannii genomes carrying KL26 and one carrying the novel KL148 gene cluster, indicating the rare occurrence of β-GlcpNAc-(1 → 2)-α-Manp in A. baumannii CPS structures. However, K26 shares a β-D-Glcp-(1 → 3)-α-L-6dTalp-(1 → 3)-β-D-GlcpNAc trisaccharide fragment with a group of related A. baumannii CPSs that have varying patterns of acetylation of L-6dTalp.</p

New <i>Obolenskvirus</i> Phages Brutus and Scipio: Biology, Evolution, and Phage-Host Interaction

Two novel virulent phages of the genus Obolenskvirus infecting Acinetobacter baumannii, a significant nosocomial pathogen, have been isolated and studied. Phages Brutus and Scipio were able to infect A. baumannii strains belonging to the K116 and K82 capsular types, respectively. The biological properties and genomic organization of the phages were characterized. Comparative genomic, phylogenetic, and pangenomic analyses were performed to investigate the relationship of Brutus and Scipio to other bacterial viruses and to trace the possible origin and evolutionary history of these phages and other representatives of the genus Obolenskvirus. The investigation of enzymatic activity of the tailspike depolymerase encoded in the genome of phage Scipio, the first reported virus infecting A. baumannii of the K82 capsular type, was performed. The study of new representatives of the genus Obolenskvirus and mechanisms of action of depolymerases encoded in their genomes expands knowledge about the diversity of viruses within this taxonomic group and strategies of Obolenskvirus–host bacteria interaction