Abstract
A recently isolated phage, vB_EcoP_SU10 (SU10), with the unusual elongated C3 morphotype, can infect a wide range of Escherichia coli strains. We have sequenced the genome of this phage and characterized it further by mass spectrometry based proteomics, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and ultra-thin section electron microscopy. The genome size is 77,327 base pairs and its genes, and genome architecture, show high similarity to the phiEco32 phage genes and genome. The TEM images reveal that SU10 have a quite long tail for being a Podoviridae phage, and that the tail also changes conformation upon infection. The ultra-thin section electron microscopy images of phages at the stage of replication within the host cell show that the phages form a honeycomb-like structure under packaging of genomes and assembly of mature capsids. This implies a tight link between the replication and cutting of the concatemeric genome, genome packaging, and capsid assembly. We have also performed a phylogenetic analysis of the structural genes common between Podoviridae phages of the C1 and C3 morphotypes. The result shows that the structural genes have coevolved, and that they form two distinct groups linked to their morphotypes. The structural genes of C1 and C3 phages appear to have diverged around 280 million years ago applying a molecular clock calibrated according to the presumed split between the Escherichia – Salmonella genera.
Highlights
Phages are considered to be the most abundant form of life on earth since the number of phages in the biosphere has been estimated to be in the order of 1031 [1, 2]
Transmission electron microscopy (TEM) studies of the selected phages revealed a phage with the rare C3 morphology of the Podoviridae family, which we named vB_EcoP_SU10 or SU10 for short
Other analysed C3 phages growing on Gram negative enterobacteria include the Serratia marcescens phage KSP100 isolated in Japan [7], The Salmonella enterica Newport phage 7–11 [8, 9] and the Cronobacter sakazakii phage vB_CsaP_GAP52 isolated in Canada (NCBI NC_019402.1), and the E. coli phage NJ01 isolated in China [10]
Summary
Phages are considered to be the most abundant form of life on earth since the number of phages in the biosphere has been estimated to be in the order of 1031 [1, 2]. Transmission electron microscopy (TEM) studies of the selected phages revealed a phage with the rare C3 morphology of the Podoviridae family, which we named vB_EcoP_SU10 or SU10 for short. Phages belonging to this morphotype have been found to infect bacteria belonging to two distantly related groups: Gramnegative enteric bacteria and Gram-positive lactococci [4]. They have an elongated head of about 90–223 nm long, varying in length from phage to phage, and a short tail [5] (Fig. 1). Its head is much longer than the heads of the phages infecting enterobacteria, and its genome and genes show no similarity to the other C3 phages mentioned
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