Friunavirus Phage-Encoded Depolymerases Specific to Different Capsular Types of Acinetobacter baumannii

Abstract

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.

The Acinetobacter baumannii K70 and K9 capsular polysaccharides consist of related K-units linked by the same Wzy polymerase and cleaved by the same phage depolymerases

“…To determine whether the difference in first sugar influences the ability of phage to recognize, bind, and digest the CPS, the activity of three different bacteriophages, AM24 ( 54 ), BS46 ( 7 , 55 ), and APK09 ( 56 ), previously shown to infect only K9-producing A. baumannii isolates among a panel of diverse K types, was tested against SGH0807. All three K9-specific phages were found to form zones of clearing on the bacterial lawn of A. baumannii SGH0807 ( Fig.…”

“… Bacteriophage and depolymerase activity on K70 CPS. ( A ) K9-specific AM24 ( 54 ), BS46 ( 7 , 55 ), and APK09 ( 56 ) phage zones of clearing on a lawn of A. baumannii SGH0807. ( B ) Oligosaccharide fragments OS1 and OS2 produced by cleavage of K70 CPS from A. baumannii SGH0807 by recombinant depolymerase (Dpo) from AM24 and APK09.…”

“…While none of the resulting zones of clearing formed by the phage had visible halos surrounding them suggestive of depolymerase activity ( 6 , 57 ), all three phages have been previously reported to encode a Dpo enzyme ( 7 , 54 – 56 ) with the Dpo from BS46 (DpoBS46) having been demonstrated to hydrolyze the K9 CPS via cleavage of the specific linkage formed by Wzy KL9 ( 7 ). DpoBS46 (BS46_gp47, GenPept accession number QEP53229.1 ) shares 73.9% aa sequence identity with DpoAM24 (AM24_gp50, GenPept accession number APD20249.1 ) over 622 of 842 aa of the protein sequence, with greater homology (92%) over the last 609 aa, which is the region responsible for CPS substrate recognition.…”

“…Purified K70 CPS was therefore treated with the previously reported recombinant depolymerases from AM24 ( 54 ) and APK09 ( 56 ) to determine whether DpoAM24 and DpoAPK09 could hydrolyze the K70 CPS. As the C-terminal region responsible for CPS recognition is highly similar in DpoAM24 and DpoBS46, digestion with DpoBS46 was not performed.…”

“…Phage BS46 was received from the Félix d’Hérelle Reference Centre for Bacterial Viruses at Laval University (Québec, Canada). Phage APK09 was isolated in 2018 and detailed described previously ( 56 ).…”