Hormogonium

Hormogonia are motile filaments of cells formed by some cyanobacteria in the order Nostocales and Stigonematales.

In response to a hormogonium-inducing factor (HIF) secreted by plant hosts, cyanobacterial symbionts differentiate into hormogonia and then dedifferentiate back into vegetative cells after about 96 hours.

The bacteria then differentiate specialized nitrogen-fixing cells called heterocysts and enter into a working symbiosis with the plant.

Depending on species, Hormogonia can be many hundreds of micrometers in length and can travel as fast as 11 μm/s.

They move via gliding motility, requiring a wettable surface or a viscous substrate, such as agar for motion.