Abstract
BackgroundThe flagellotropic phage 7-7-1 infects motile cells of Agrobacterium sp H13-3 by attaching to and traveling along the rotating flagellar filament to the secondary receptor at the base, where it injects its DNA into the host cell. Here we describe the complete genomic sequence of 69,391 base pairs of this unusual bacteriophage.MethodsThe sequence of the 7-7-1 genome was determined by pyro(454)sequencing to a coverage of 378-fold. It was annotated using MyRAST and a variety of internet resources. The structural proteome was analyzed by SDS-PAGE coupled electrospray ionization-tandem mass spectrometry (MS/MS).ResultsSequence annotation and a structural proteome analysis revealed 127 open reading frames, 84 of which are unique. In six cases 7-7-1 proteins showed sequence similarity to proteins from the virulent Burkholderia myovirus BcepB1A. Unique features of the 7-7-1 genome are the physical separation of the genes encoding the small (orf100) and large (orf112) subunits of the DNA packaging complex and the apparent lack of a holin-lysin cassette. Proteomic analysis revealed the presence of 24 structural proteins, five of which were identified as baseplate (orf7), putative tail fibre (orf102), portal (orf113), major capsid (orf115) and tail sheath (orf126) proteins. In the latter case, the N-terminus was removed during capsid maturation, probably by a putative prohead protease (orf114).
Highlights
The flagellotropic phage 7-7-1 infects motile cells of Agrobacterium sp H13-3 by attaching to and traveling along the rotating flagellar filament to the secondary receptor at the base, where it injects its DNA into the host cell
Filament associated phage particles initially possess DNA-filled heads, which are subsequently found emptied when attached to the phage receptor at the flagellar base
Differences between the two flagellotropic phages are reflected by their distinct morphologies: electron micrographs of phage χ show a single long (200–220 nm) tail fiber wrapped around the ‘plain’ filament of Salmonella [7], whereas phage 7-7-1 exhibits five short (16 nm) tail fibers with splayed tips
Summary
The flagellotropic phage 7-7-1 infects motile cells of Agrobacterium sp H13-3 by attaching to and traveling along the rotating flagellar filament to the secondary receptor at the base, where it injects its DNA into the host cell. Filament associated phage particles initially possess DNA-filled heads, which are subsequently found emptied when attached to the phage receptor at the flagellar base. This bimodal mechanism of adsorption dramatically increases the chance for finding the receptor at the cell surface, because (i). Such conditions are not met by the ‘complex’ flagella of Agrobacterium sp H13-3.
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