Bacteriophages are the most abundant biological entity on earth, engaged in a repeated cycle of infection and replication within their bacterial hosts. Bacteria are not helpless in this struggle, and have ample means of defending themselves against phage predation. This puts bacteriophages under selective pressure to remain infectious and adapt extensively. Phages infecting members of the Acinetobacter and Campylobacter genera are of interest because of their hosts’ pathogenicity and diverse array of glycoconjugates available for phage interaction. In this study, three Acinetobacter species were isolated, including the phage-propagating strain A. radioresistens, LH6, along with two dsDNA Podoviridae and five dsRNA Cystoviridae. Characterizing the structural components of Cystovirus CAP3 revealed an unknown high-molecular-weight polysaccharide and a low-molecular-weight lipid-linked glycoconjugate. Further studies examining phage interactions with their multidrug resistant hosts demonstrated two mechanisms for the release of antimicrobial resistance determinants, through phage lysis, and through contact dependent killing by A. baumanni. These findings, specifically the ability for phage to release intact resistance determinants, in the form of DNA, raised interesting questions about how bacteriophages interact with their host cells after infection. In particular, we examined how phage infection affects intracellular nucleotide pools using C. jeuni and representative Fletchervirus and Firehammervirus phages as our model systems. Unexpectedly, we discovered that genomic guanosine is replaced with inosine or 7-amido-7-deazaguanosine (ADG) in the respective phages, each employing independent mechanisms of modification, with inosine replacement occurring during genome replication, and ADG replacing guanosine after genome replication. While studying the impacts of phage infection on C. jejuni nucleotide metabolism, efforts were also made to study the impact of another abundant metabolite, trehalose, in Acinetobacter. Trehalose is a glucose disaccharide, which contributes to virulence and possible DNA protection in A. baumannii. Without this simple metabolite, A. baumannii showed increased sensitivity to desiccation, colistin, serum bactericidal activity, and opsonophagocytosis, with decreased membrane integrity and capsule expression. Together, these findings contribute to the knowledge on Acinetobacter and Campylobacter pathogenesis, and the phage adaptations necessary to replicate within their bacterial hosts.
