Arpless comets are fascin-ating

Actin elongation is a force to be reckoned with. Results on page 233 by Brieher et al. show that elongating bundles of actin can, by themselves, propel a bacterium, and do so faster than frequent actin nucleation does.

Actin filament nucleation by Arp2/3 is a prerequisite for movement of the intracellular pathogen Listeria monocytogenes. Through repeated nucleations, Arp2/3 builds a comet tail of short branched actin filaments that push the bug from behind. But Brieher and colleagues show that once some nucleation occurs, comet tails can be built without Arp2/3.

Upon Arp2/3 inhibition, the branched filaments elongated into long barrel-shaped tails encircling the bacterium. Bugs building these structures were faster than those using Arp2/3. As the barrels are not attached at the bug's rear, it is not clear how movement is achieved. Fractionation...