Abstract
Tailed viruses are the most common isolates infecting prokaryotic hosts residing in hypersaline environments. Archaeal tailed viruses represent only a small portion of all characterized tailed viruses of prokaryotes. But even this small dataset revealed that archaeal tailed viruses have many similarities to their counterparts infecting bacteria, the bacteriophages. Shared functional homologs and similar genome organizations suggested that all microbial tailed viruses have common virion architectural and assembly principles. Recent structural studies have provided evidence justifying this thereby grouping archaeal and bacterial tailed viruses into a single lineage. Currently there are 17 haloarchaeal tailed viruses with entirely sequenced genomes. Nine viruses have at least one close relative among the 17 viruses and, according to the similarities, can be divided into three groups. Two other viruses share some homologs and therefore are distantly related, whereas the rest of the viruses are rather divergent (or singletons). Comparative genomics analysis of these viruses offers a glimpse into the genetic diversity and structure of haloarchaeal tailed virus communities.
Highlights
Tailed viruses are the most common isolates infecting prokaryotic hosts residing in hypersaline environments
The aim of this review is to summarize the findings on the 13 new complete haloarchaeal tailed virus genomes that were published in three separate papers (Pietilä et al, 2013b,c; Sencilo et al, 2013) and to combine these data with the previous knowledge of the complete genomes of haloarchaeal tailed viruses
Tailed bacteriophages are classified into order Caudovirales, which is further divided into three families according to the tail morphology: Myoviridae characterized by long contractile tails, Siphoviridae and Podoviridae (King et al, 2012)
Summary
The situation changed partly due to the recent technological advancements that have made for instance the sequencing of viral genomes much cheaper and faster than before This caused an exponential increase in the number of sequencing projects focusing on separate virus genomes or on metaviromes from hypersaline environments (Santos et al, 2010; Boujelben et al, 2012; GarciaHeredia et al, 2012; Pietilä et al, 2013b,c; Sencilo et al, 2013). CLASSIFICATION OF PROKARYOTIC TAILED VIRUSES Tailed euryarchaeal (including haloarchaeal) viruses have been shown to have many properties in common with their bacterial counterparts, the bacteriophages, starting from the morphology and the genome structure to gene regulation and some protein homologs (Torsvik and Dundas, 1974; Stolt and Zillig, 1994; Porter et al, 2007).
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