Hormogonium
Encyclopedia
Hormogonia are motile filaments of cells formed by some cyanobacteria in the family Nostoceae. They are formed during asexual reproduction in unicellular, filamentous cyanobacteria some contain heterocysts and akinetes
.
Cyanobacteria differentiate into hormogonia when exposed to an environmental stress or when placed in new media.
Hormogonium differentiation is crucial for the development of nitrogen-fixing
plant cyanobacteria symbioses, in particular that between cyanobacteria of the genus Nostoc
and their host
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
, requiring a wet-able surface or a viscous substrate, such as agar
for motion.
Akinete
An akinete is a thick-walled dormant cell derived from the enlargement of a vegetative cell. It serves as a survival structure. It is a resting cell of cyanobacteria and unicellular and filamentous green algae. Under magnification, akinetes appear thick walled with granular-looking cytoplasms....
.
Cyanobacteria differentiate into hormogonia when exposed to an environmental stress or when placed in new media.
Hormogonium differentiation is crucial for the development of nitrogen-fixing
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
plant cyanobacteria symbioses, in particular that between cyanobacteria of the genus Nostoc
Nostoc
Nostoc is a genus of cyanobacteria found in a variety of environmental niches that forms colonies composed of filaments of moniliform cells in a gelatinous sheath.The name "Nostoc" was invented by Paracelsus...
and their host
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
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
Bacterial gliding
Bacterial gliding is a process whereby a bacterium can move under its own power. This process does not involve the use of flagella, which is a more common means of motility in bacteria...
, requiring a wet-able surface or a viscous substrate, such as agar
Agar
Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...
for motion.