Specific Interaction of NovelFriunavirusPhages Encoding Tailspike Depolymerases with Corresponding Acinetobacter baumannii Capsular Types

Abstract

Acinetobacter baumannii is one of the most clinically important nosocomial pathogens. The World Health Organisation refers it to its «critical priority» category to develop new strategies for effective therapy. This microorganism is capable of producing structurally diverse capsular polysaccharides (CPSs), which serve as primary receptors for A. baumannii bacteriophages carrying polysaccharide-depolymerasing enzymes. In this study, eight novel bacterial viruses that specifically infect A. baumannii strains belonging to K2/K93, K32, K37, K44, K48, K87, K89 and K116 capsular types were isolated and characterized. The overall genomic architecture demonstrated that these viruses are representatives of the Friunavirus genus of the family Autographiviridae. The linear double-stranded DNA phage genomes of 41,105–42,402 bp share high nucleotide sequence identity, except for genes encoding structural depolymerases or tailspikes which determine the host specificity. Deletion mutants lacking N-terminal domains of tailspike proteins were cloned, expressed and purified. The structurally defined CPSs of the phage bacterial hosts were cleaved with the specific recombinant depolymerases, and the resultant oligosaccharides that corresponded to monomers or/and dimers of the CPS repeats (K-units) were isolated. Structures of the derived oligosaccharides were established by nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectrometry. The data obtained showed that all depolymerases studied were glycosidases that cleave specifically the A. baumannii CPSs by the hydrolytic mechanism, in most cases, by the linkage between the K-units. IMPORTANCE Acinetobacter baumannii, a nonfermentative, Gram-negative, aerobic bacterium, is one of the most significant nosocomial pathogens. The pathogenicity of A. baumannii is based on the cooperative action of many factors, one of them being the production of capsular polysaccharides (CPSs) that surround bacterial cells with a thick protective layer. Polymorphism of the chromosomal capsule loci is responsible for the observed high structural diversity of the CPSs. In this study, we describe eight novel lytic phages which have different tailspike depolymerases (TSDs) determining the interaction of the viruses with corresponding A. baumannii capsular types (K-types). Moreover, we elucidate the structures of oligosaccharide products obtained by cleavage of the CPSs by the recombinant depolymerases. We believe that as the TSDs determine phage specificity, the diversity of their structures should be taken into consideration as selection criteria for inclusion of certain phage candidate to the cocktail designed to control A. baumannii with different K-types.

Phage φAB6-Borne Depolymerase Combats Acinetobacter baumannii Biofilm Formation and Infection

“…It is known that the phage tail fiber or tail spike protein often functions as a polysaccharide depolymerase and targets specific capsule types for enhancing the antivirulence activity [ 41 ]. In A. baumannii , more than 128 types of capsule loci (KL type) have been identified, so even though many phages depolymerase functions have been studied [ 28 , 30 , 37 , 42 , 43 , 44 ], unlike broad-spectrum bactericidal antibiotics, they still target only a limited number of bacterial strains. Therefore, identification of novel depolymerases and evaluation of their ability to control A. baumannii infections is important.…”

Novel Acinetobacter baumannii Myovirus TaPaz Encoding Two Tailspike Depolymerases: Characterization and Host-Recognition Strategy

“…The latent period for TaPaz was about 30 min, and the burst size was approximately 110 particles per infected cell. The host specificity of TaPaz was tested against a collection of A. baumannii strains with biochemically characterized CPS structures belonging to 56 different K types used in our previous study [5] (Table S1). It was found that TaPaz was highly specific as the other depolymerase-carrying A. baumannii phages and was cable to infect only a strain with a certain CPS structure, namely A. baumannii NIPH601 of K47 capsular type.…”

“…On the example of several previously characterized A. baumannii phages, it was shown that TSDs encoding in their genomes are responsible for the ability of bacterial viruses to infect the strains with certain CPS structures [5][6][7][8][9][10]12]. Genes encoding two different TSDs that presumably allow TaPaz to infect the representatives of two various Acinetobacter K types were identified in the phage genome.…”

“…The structures of the CPSs produced by A. baumannii are highly diverse, more than 140 capsular types (K types) have been bioinformatically predicted (J.J. Kenyon, Queensland University of Technology, Brisbane, Australia, personal communication), and the CPS structures for more than 40 capsular types (K types) have been biochemically established [5]. CPSs are the primary receptors for A. baumannii-phages that carry genes encoding polysaccharide-degrading enzymes or structural depolymerases [5][6][7][8]. Thus, phage depolymerases determine specific interactions of phages with bacterial hosts producing CPS of a certain structure.…”

“…Thus, phage depolymerases determine specific interactions of phages with bacterial hosts producing CPS of a certain structure. To date, phages that are specific to K1 (phage P1) [9], K2 (phages vB_AbaP_APK2, ϕAB6, and vB_AbaP_B3) [5,7,9], K9 (phages vB_AbaP_B1, AM24, BS46) [9][10][11], K19 (phages Fri1 and AS11) [12], K27 (phage AS12) [12], K32 (phage vB_AbaP_APK32) [5], K37 (phage vB_AbaP_APK37) [5], K44 (phage vB_AbaP_APK44) [5], K45 (phage vB_AbaM_B9) [8], K48 (phage vB_AbaP_APK48) [5], K87 (phage vB_AbaP_APK87) [5], K89 (phage vB_AbaP_APK89) [5], K91 (phage AP22) [13], K93 (phages vB_AbaP_APK2 and vB_AbaP_APK93) [5], and K116 (phage vB_AbaP_APK116) [5] capsular types of A. baumannii have been isolated and described. Genomes of all phages listed above encode only one tailspike depolymerase (TSD) specific to a certain K type or two K types with similar structures (for example K2/K93 in the case of phage vB_AbaP_APK2).…”