Hormogonium

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

They are formed during vegetative reproduction in unicellular, filamentous cyanobacteria, and some may contain heterocysts and akinetes.

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.

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