Novel Cluster AZArthrobacterphages Powerpuff, Lego, and YesChef exhibit close functional relationships withMicrobacteriumphages

Abstract

Bacteriophages exhibit a vast spectrum of relatedness and there is increasing evidence of close genomic relationships independent of host genus. The variability in phage similarity at the nucleotide, amino acid, and gene content levels confounds attempts at quantifying phage relatedness, especially as more novel phages are isolated. This study describes three highly similar novel Arthrobacter globiformis phages–Powerpuff, Lego, and YesChef–which were assigned to Cluster AZ using a nucleotide-based clustering parameter. Phages in Cluster AZ and Microbacterium Cluster EH, as well as the former Microbacterium singleton Zeta1847, exhibited low nucleotide similarity but gene content similarity in excess of the recently adopted Microbacterium clustering parameter, which resulted in the reassignment of Zeta1847 to Cluster EH. Additionally, while Clusters AZ and EH phages lack identifiable repressors or partitioning systems typically required for lysogeny, they encode a shared integrase indicative of a lysogenic life cycle. In the first experimental verification of a Cluster AZ phage’s life cycle, we show that phage Powerpuff is a true temperate phage and forms stable lysogens. Moreover, we provide evidence that Clusters AZ and EH phages exhibit similar genome architectures in addition to their shared integrases, suggesting that these phages may all be temperate and undergo an unknown lysogeny mechanism. Our findings further highlight the importance of using multiple metrics to capture phage relatedness and provide additional evidence of significant shared phage genomic content spanning multiple actinobacterial host genera.