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The type of capsular polysaccharide (CPS) on the cell surface of Acinetobacter baumannii can determine the specificity of lytic bacteriophage under consideration for therapeutic use. Here, we report the isolation of a phage on an extensively antibiotic resistant ST2 A. baumannii isolate AB5001 that carries the KL3 CPS biosynthesis gene cluster predicting a K3-type CPS. As the phage did not infect isolates carrying KL3 or KL22 and known to produce K3 CPS, the structure of the CPS isolated from A. baumannii AB5001 was determined. AB5001 produced a variant CPS form, K3-v1, that lacks the β-d-GlсpNAc side chain attached to the d-Galp residue in the K3 structure. Inspection of the KL3 sequence in the genomes of AB5001 and other phage-susceptible isolates with a KL3 locus revealed single-base deletions in gtr6, causing loss of the Gtr6 glycosyltransferase that adds the missing d-GlсpNAc side chain to the K3 CPS. Hence, the presence of this sugar profoundly restricts the ability of the phage to digest the CPS. The 41-kb linear double-stranded DNA (dsDNA) phage genome was identical to the genome of a phage isolated on a K37-producing isolate and thus was named APK37.1. APK37.1 also infected isolates carrying KL116. Consistent with this, K3-v1 resembles the K37 and K116 structures. APK37.1 is a Friunavirus belonging to the Autographiviridae family. The phage-encoded tail spike depolymerase DpoAPK37.1 was not closely related to Dpo encoded by other sequenced Friunaviruses, including APK37 and APK116. IMPORTANCE Lytic bacteriophage have potential for the treatment of otherwise untreatable extensively antibiotic-resistant bacteria. For Acinetobacter baumannii, most phage exhibit specificity for the type of capsular polysaccharide (CPS) produced on the cell surface. However, resistance can arise via mutations in CPS genes that abolish this phage receptor. Here, we show that single-base deletions in a CPS gene result in alteration of the final structure rather than deletion of the capsule layer and hence affect the ability of a newly reported podophage to infect strains producing the K3 CPS.

Acinetobacter baumannii, capsular polysaccharide, K locus, APK37.1, K3-v1, KL3

NCBI PubMed ID: 36651782
Publication DOI: 10.1128/spectrum.03631-22
Journal NLM ID: 101634614
Publisher: Washington, DC: ASM Press
Correspondence: J.J.Kenyon
Institutions: N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia, Central Scientific Research Institute of Epidemiology, Moscow, Russia, Centre for Immunology and Infection Control, School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Australia, State Research Center for Applied Microbiology and Biotechnology, Obolensk, Russia, M. M. Shemyakin and Yu. A. Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia, School of Life and Environmental Science, University of Sydney, Sydney, Australia
Methods: 13C NMR, 1H NMR, NMR-2D, chemical analysis, GLC, Smith degradation, de-O-acetylation, GPC, bioinformatic analysis, phage isolation, phage propagation, phage sequencing

Acinetobacter baumannii is a critical priority nosocomial pathogen that produces a variety of capsular polysaccharides (CPSs), the primary receptors for specific depolymerase-carrying phages. In this study, the tailspike depolymerases (TSDs) encoded in genomes of six novel Friunaviruses, APK09, APK14, APK16, APK86, APK127v, APK128, and one previously described Friunavirus phage, APK37.1, were characterized. For all TSDs, the mechanism of specific cleavage of corresponding A. baumannii capsular polysaccharides (CPSs) was established. The structures of oligosaccharide fragments derived from K9, K14, K16, K37/K3-v1, K86, K127, and K128 CPSs degradation by the recombinant depolymerases have been determined. The crystal structures of three of the studied TSDs were obtained. A significant reduction in mortality of Galleria mellonella larvae infected with A. baumannii of K9 capsular type was shown in the example of recombinant TSD APK09_gp48. The data obtained will provide a better understanding of the interaction of phage-bacterial host systems and will contribute to the formation of principles of rational usage of lytic phages and phage-derived enzymes as antibacterial agents.

Acinetobacter baumannii, capsular polysaccharide, crystal structure, bacteriophage, glycosidase, capsular type, tailspike depolymerase

NCBI PubMed ID: 37240444
Publication DOI: 10.3390/ijms24109100
Journal NLM ID: 101092791
Publisher: Basel, Switzerland: MDPI
Correspondence: A.V. Popova
Institutions: Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, 117997 Moscow, Russia, State Research Center for Applied Microbiology and Biotechnology, 142279 Obolensk, Russia, N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russia, Bach Institute of Biochemistry, Research Centre of Biotechnology of the Russian Academy of Sciences, 119071 Moscow, Russia, Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 141700 Dolgoprudny, Russia, Complex of NBICS Technologies, National Research Center 'Kurchatov Institute', 123182 Moscow, Russia, Central Scientific Research Institute of Epidemiology, 111123 Moscow, Russia
Methods: 13C NMR, 1H NMR, NMR-2D, PCR, X-ray, DNA techniques, GPC, enzymatic depolymerization, crystallization, HR-ESI-MS, phage isolation, phage genome analysis, phage propagation, phage sequencing

Acinetobacter baumannii, capsular polysaccharide, crystal structure, bacteriophage, glycosidase, capsular type, tailspike depolymerase