Not a bad hair day for Phage 7-7-1

(click to enlarge)
Cryo-electron tomography and segmentation of phage 7-7-1 attached to Agrobacterium flagellum. (b) Example of long flexible fibers (white arrow) of a full-capsid phage 7-7-1, originating from the capsid vertices. (c) Occasionally, it can be observed that the flexible capsid fibers are connecting two phages (white arrow). (d) The interaction of two phage capsid fibers with the host flagellum (red arrows). (e) Two phages attached to the same flagellum (green arrows), further emphasizing the strong interaction between phage 7-7-1 and the host flagellum. (f) A volumetric representation of the tomo­gram subregion shown in e, with manual segmentation performed using IMOD. Scale bar: 50 nm. Source

Noteworthy
 

Noteborn et al. (2025) say in the introduction to their very recent paper (preprint): "Flagello­tropic bacteriophages represent a distinct group of phages that initiate their infection cycle by attaching to the flagellum of their motile host." One such “flagellotropic bacteriophage” is the E. coli phage χ (Chi), which was featured by Michael Yarmolinski in A fastidious Bacteriophage, and Elio & Merry mentioned another one, the B. subtilis phage PBS1, in the same STC post.
 

While the phages χ and PBS1 attach to the flagella of their hosts via the tail fibers, phage 7-7-1 of Agrobacterium sp. H13-3 has another trick up its sleeve – or better: on its head (capsid). No­teborn et al. found that phage 7-7-1 (genome size: 247 kbp) sports a bunch of dreadlocks on its head, proteinaceous fibers with which it attaches to host flagella (see Figure). This is not un­precedented, as phage φCbK also attaches via its head to the flagella of its host Caulobacter, as reported by Merry in Now That's Using Your Head!  However, unlike phage 7-7-1 with its dreadlocks all tangled up in a flagellum, phage φCbK sports a single long fibre on its head that makes it look more like the beloved comic character Tintín by the Belgian cartoonist Hergé. Take-home lesson: phages are quite creative and don't always catch their host cells by their tails.
 

 

("Noteworthy" is the new format for STC's Thursday posts. Please read our Jan 20, 2025 post outlining this and other changes in our blog.)

 

 

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