A Novel Genus of Actinobacterial Tectiviridae

Steven M Caruso,Anthony Huynh,Shabnam Parsa,George Morcos,Nansen Kuo,Ivan Erill,Tagide N Decarvalho

doi:10.3390/v11121134

Abstract

Streptomyces phages WheeHeim and Forthebois are two novel members of the Tectiviridae family. These phages were isolated on cultures of the plant pathogen Streptomyces scabiei, 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. Streptomyces phages WheeHeim and Forthebois have linear dsDNA chromosomes (18,266 bp and 18,251 bp long, respectively) with the characteristic two-segment architecture of the Tectiviridae. 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 Rhodococcus phage Toil, form a new genus within the Tectiviridae, which we have tentatively named Deltatectivirus. 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 Tectiviridae are an ancient lineage infecting a broad range of bacterial hosts.

Highlights

The Tectiviridae are a family of tail-less double-stranded DNA phages characterized by an internal protein-rich lipid membrane enclosed within a non-enveloped icosahedral proteinaceous capsid [1,2]
Streptomyces phages WheeHeim and Forthebois were extracted from soil samples with phage buffer (10 mM Tris pH 7.5, 10 mM MgSO4, 1 mM CaCl2, 68.5 mM NaCl) and filtered through a 0.22 μm filter. 500 μL of the filtrate was added to 250 μL of a 48 h culture of Streptomyces scabiei RL-34 (ATCC 49173), incubated 10 min at room temperature, combined with 4 mL of tryptic soy soft agar (BD), overlaid on nutrient agar (BD Difco) supplemented with 10 mM MgCl2, 8 mM Ca(NO3 )2, and
Intergenomic protein sequence distances were computed with 100 pseudo-bootstrap replicates using the Genome-BLAST Distance Phylogeny (GBDP) method optimized for prokaryotic viruses [54,55], and a minimum evolution tree was computed with FASTME on the resulting intergenomic distances [56]

Summary

Introduction

The Tectiviridae are a family of tail-less double-stranded DNA (dsDNA) phages characterized by an internal protein-rich lipid membrane enclosed within a non-enveloped icosahedral proteinaceous capsid [1,2]. Tectiviruses bind to the host cell surface via receptor binding proteins integrated into the spikes that protrude from each capsid vertex [3]. After adsorbing to the host cell, the tectiviral membrane vesicle is reorganized to generate a tubular structure. This nanotube protrudes from one of the capsid vertices in order to inject the viral DNA [4,5].

Methods

Results

Conclusion