A Novel Genus of Actinobacterial Tectiviridae

Abstract

<i>Streptomyces phages WheeHeim</i> and <i>Forthebois</i> are two novel members of the <i>Tectiviridae</i> family. These phages were isolated on cultures of the plant pathogen <i>Streptomyces scabiei</i>, known for its worldwide economic impact on potato crops. Transmission electron microscopy showed viral particles with double-layered icosahedral capsids, and frequent instances of protruding nanotubes harboring a collar-like structure. Mass-spectrometry confirmed the presence of lipids in the virion, and serial purification of colonies from turbid plaques and immunity testing revealed that both phages are temperate. <i>Streptomyces</i><i>phages WheeHeim</i> and <i>Forthebois</i> have linear dsDNA chromosomes (18,266 bp and 18,251 bp long, respectively) with the characteristic two-segment architecture of the <i>Tectiviridae</i>. Both genomes encode homologs of the canonical tectiviral proteins (major capsid protein, packaging ATPase and DNA polymerase), as well as PRD1-type virion-associated transglycosylase and membrane DNA delivery proteins. Comparative genomics and phylogenetic analyses firmly establish that these two phages, together with <i>Rhodococcus</i><i>phage Toil</i>, form a new genus within the <i>Tectiviridae</i>, which we have tentatively named <i>Deltatectivirus</i>. The identification of a cohesive clade of Actinobacteria-infecting tectiviruses with conserved genome structure but with scant sequence similarity to members of other tectiviral genera confirms that the <i>Tectiviridae</i> are an ancient lineage infecting a broad range of bacterial hosts.