Motility in cyanobacteria: polysaccharide tracks and Type IV pilus motors

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Abstract

Summary

Motility in cyanobacteria is useful for purposes that range from seeking out favourable light environments to establishing symbioses with plants and fungi. No known cyanobacterium is equipped with flagella, but a diverse range of species is able to ‘glide’ or ‘twitch’ across surfaces. Cyanobacteria with this capacity range from unicellular species to complex filamentous forms, including species such asNostoc punctiforme, which can generate specialised motile filaments called hormogonia. Recent work on the model unicellular cyanobacteriumSynechocystissp. PCC 6803 has shown that its means of propulsion has much in common with the twitching motility of heterotrophs such asPseudomonasandMyxococcus. Movement depends on Type IV pili, which are extended, adhere to the substrate and then retract to pull the cell across the surface. Previous work on filamentous cyanobacteria suggested a very different mechanism, with movement powered by the directional extrusion of polysaccharide from pores close to the cell junctions. Now a new report by Khayatan and colleagues in this issue of Molecular Microbiology suggests that the motility ofNostochormogonia has much more in common withSynechocystisthan was previously thought. In both cases, polysaccharide secretion is important for preparing the surface, but the directional motive force comes from Type IV pili.

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