Characterization of novel Actinobacteriophage Giantsbane reveals unexpected cluster AU relationships

Bacteriophages that infect Arthrobacter, a genus of bacteria which play key ecological roles in soil, warrant further study. Giantsbane, a novel Actinobacteriophage, was isolated using Arthrobacter globiformis as a host. Transmission electron microscopy and whole-genome sequencing revealed a Siphoviridae morphology and a genome length of 56,734 bp. Genome annotation identified 94 putative genes, such as a duplicated major tail protein and a major capsid and protease fusion protein. No genes were associated with lysogeny, indicating a lytic phage. Giantsbane was assigned to the phage cluster AU. Batch average nucleotide identity analysis and phylogenetic networks constructed from shared genes revealed unexpected nucleotide and gene content similarities within cluster AU. These findings have resulted in the creation of two new AU subclusters and the resubclustering of three AU bacteriophages. Analysis using Phamerator and MEME identified repeated motifs and a gene cassette present in all evaluated cluster AU phages which may promote recombination. These findings offer the first intra-cluster analysis of cluster AU phages and further our understanding of the relationships between closely related bacteriophages.