Other phage use bacterial appendages in an even more clever way. These φCb13 siphophage take advantage of the cell’s motility to hitch a ride to the cell. They have a filament on their head that wraps into the helical groove of the Caulobacter crescentus flagellum. Remember that flagella can spin either clockwise or counter-clockwise. If this single polar flagellum spins clockwise, pushing the cell body, the attached phage would unscrew like a nut off the end of the flagellum. But if the flagellum spins counter-clockwise, the nut will instead spin down to the cell body, where its tail fibers will find their receptors and its tail will inject the genome (⇩).
Here you see several φCb13 phage that have successfully reached their target receptors at the pole of a Caulobacter crescentus and are in the process of infecting the cell (note the mix of filled capsids that have not yet released their genome and empty capsids that have). This particularly unlucky cell has already been infected by a different kind of phage, as you can see from the capsids assembling inside (more on that process on the next page).
