hormogonium

Hormogonia are motile filaments of cells formed by some

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue ...

in the order

Nostocales The Nostocales are an order of cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly for ...

and

Stigonematales The Rivulariaceae are a family of cyanobacteria within the Nostocales in which the filaments (trichomes) are tapered from wider at the base to narrower at the tip. The type species is '' Rivularia haematites'' (Dc) C. A. Agardh. Genera , WoR ...

. They are formed during vegetative reproduction in unicellular, filamentous

, and some may contain

heterocyst Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as '' Nostoc punctiforme'', '' Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen f ...

s and

akinete An akinete is an enveloped, thick-walled, non-motile, dormant cell formed by filamentous, heterocyst-forming cyanobacteria under the order Nostocales and Stigonematales. Akinetes are resistant to cold and desiccation. They also accumulate and sto ...

s. Cyanobacteria differentiate into hormogonia when exposed to an

environmental stress Stress, either physiological, biological or psychological, is an organism's response to a stressor such as an environmental condition. Stress is the body's method of reacting to a condition such as a threat, :wikt:challenge, challenge or physic ...

or when placed in new media. Hormogonium differentiation is crucial for the development of

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...

plant cyanobacteria symbioses, in particular that between cyanobacteria of the genus ''

Nostoc ''Nostoc'', also known as star jelly, troll’s butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch’s jelly, is the most common genus of cyanobacteria found in var ...

'' and their

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County People * Jim Host (born 1937), American businessman * Michel Hos ...

s. 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. Hopefully, they have managed to reach the plant host by this time. 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 Gliding motility is a type of translocation used by microorganisms that is independent of propulsive structures such as flagella, pili, and fimbriae. Gliding allows microorganisms to travel along the surface of low aqueous films. The mechanisms of ...

, requiring a wettable surface or a viscous substrate, such as

agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori ('' Gracilaria'') and "tengusa" ('' Gelidiaceae''). As found in nature, agar ...

for motion. Cell anatomy Cyanobacteria {{cyanobacteria-stub