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 hosts. 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 wettable surface or a viscous substrate, such as agar for motion.
Nitrogen fixation is a chemical process by which molecular nitrogen (N 2), with a strong triple covalent bond, in the air is converted into ammonia (NH 3) or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmospheric nitrogen is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms. Biological nitrogen fixation or diazotrophy is an important microbially mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif).
Cyanobacteria, also known as Cyanophyta, are a phylum of Gram-negative bacteria that obtain energy via photosynthesis. The name cyanobacteria comes from their color, giving them their other name, "blue-green algae", though modern botanists restrict the term algae to eukaryotes and do not apply it to cyanobacteria, which are prokaryotes. They appear to have originated in freshwater or a terrestrial environment. Sericytochromatia, the proposed name of the paraphyletic and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria.
Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters. Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally.Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts.
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 from dinitrogen (N2) in the air using the enzyme nitrogenase, in order to provide the cells in the filament with nitrogen for biosynthesis.
Diazotrophs are bacteria and archaea that fix atmospheric nitrogen gas into a more usable form such as ammonia.
Anabaena is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyanobacteria that produce neurotoxins, which are harmful to local wildlife, as well as farm animals and pets. Production of these neurotoxins is assumed to be an input into its symbiotic relationships, protecting the plant from grazing pressure.
Nostoc is a genus of cyanobacteria found in various environments that forms colonies composed of filaments of moniliform cells in a gelatinous sheath.
Cyanolichens are lichens that apart from the basic fungal component ("mycobiont"), contain cyanobacteria, otherwise known as blue-green algae, as the photosynthesizing component ("photobiont"). Overall, about a third of lichen photobionts are cyanobacteria and the other two thirds are green algae.
Algal mats are one of many types of microbial mat that forms on the surface of water or rocks. They are typically composed of blue-green cyanobacteria and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments are deposited or grow in place, creating dark-laminated layers. Stromatolites are prime examples of algal mats. Algal mats played an important role in the Great Oxidation Event on Earth some 2.3 billion years ago. Algal mats can become a significant ecological problem, if the mats grow so expansive or thick as to disrupt the other underwater marine life by blocking the sunlight or producing toxic chemicals.
The Nostocaceae are a family of cyanobacteria that forms filament-shaped colonies enclosed in mucus or a gelatinous sheath. Some genera in this family are found primarily in fresh water, while others are found primarily in salt water. Other genera may be found in both fresh and salt water. Most benthic algae of the order Nostocales belong to this family.
Geosiphon is a genus of fungus in the family Geosiphonaceae. The genus is monotypic, containing the single species Geosiphon pyriformis, first described by Kützing in 1849 as Botrydium pyriforme. In 1915, Von Wettstein characterized Geosiphon pyriforme as a multinucleate alga containing endosymbiotic cyanobacteria, although he also noted the presence of chitin, a component of fungal cell walls. In 1933, Knapp was the first to suggest the fungal origin of the species and described it as a lichen with endosymbiotic cyanobacteria. It is the only member of the Glomeromycota known to not form a symbiosis with terrestrial plants in the form of arbuscular mycorrhiza.
Anabaena circinalis is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in A. circinalis owes to its production of several potentially harmful cyanotoxins, ranging in potency from irritating to lethal. Under favorable conditions for growth, A. circinalis forms large algae-like blooms, potentially harming the flora and fauna of an area.
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 store various essential material, both of which allows the akinete to serve as a survival structure for up to many years. However, akinetes are not resistant to heat. Akinetes usually develop in strings with each cell differentiating after another and this occurs next to heterocysts if they are present. Development usually occurs during stationary phase and is triggered by unfavorable conditions such as insufficient light or nutrients, temperature, and saline levels in the environment. Once conditions become more favorable for growth, the akinete can then germinate back into a vegetative cell. Increased light intensity, nutrients availability, oxygen availability, and changes in salinity are important triggers for germination. In comparison to vegetative cells, akinetes are generally larger. This is associated with the accumulation of nucleic acids which is important for both dormancy and germination of the akinete. Despite being a resting cell, it is still capable of some metabolic activities such as photosynthesis, protein synthesis, and carbon fixation, albeit at significantly lower levels.
Cyanobionts are cyanobacteria that live in symbiosis with a wide range of organisms such as terrestrial or aquatic plants; as well as, algal and fungal species. They can reside within extracellular or intracellular structures of the host. In order for a cyanobacterium to successfully form a symbiotic relationship, it must be able to exchange signals with the host, overcome defense mounted by the host, be capable of hormogonia formation, chemotaxis, heterocyst formation, as well as possess adequate resilience to reside in host tissue which may present extreme conditions, such as low oxygen levels, and/or acidic mucilage. The most well-known plant-associated cyanobionts belong to the genus Nostoc. With the ability to differentiate into several cell types that have various functions, members of the genus Nostoc have the morphological plasticity, flexibility and adaptability to adjust to a wide range of environmental conditions, contributing to its high capacity to form symbiotic relationships with other organisms. Several cyanobionts involved with fungi and marine organisms also belong to the genera Richelia, Calothrix, Synechocystis, Aphanocapsa and Anabaena, as well as the species Oscillatoria spongeliae. Although there are many documented symbioses between cyanobacteria and marine organisms, little is known about the nature of many of these symbioses. The possibility of discovering more novel symbiotic relationships is apparent from preliminary microscopic observations.
Cylindrospermopsis raciborskii is a freshwater cyanobacterium.
Aulosira is a genus of cyanobacteria found in a variety of environmental niches that forms colonies composed of filaments of moniliform cells.
Nostoc punctiforme is a species of filamentous cyanobacterium. Under non-limiting nutritional environmental conditions, its filaments are composed of photosynthetic vegetative cells; upon nutrient limitation, some of these cells undergo differentiation into heterocysts, akinetes or hormogonia.
Some types of lichen are able to fix nitrogen from the atmosphere. This process relies on the presence of cyanobacteria as a partner species within the lichen. The ability to fix nitrogen enables lichen to live in nutrient-poor environments. Lichen can also extract nitrogen from the rocks on which they grow.
Richelia is a genus of nitrogen-fixing filamentous heterocystous cyanobacteria. It contains the single species Richelia intracellularis. They exist as both free-living organisms as well as symbionts within potentially up to 13 diatoms distributed throughout the global ocean. As a symbiont, Richelia can associate epiphytically and as endosymbionts within the periplasmic space between the cell membrane and cell wall of diatoms.
Cyanobacteria are a large and diverse phylum of bacteria defined by their unique combination of pigments and their ability to perform oxygenic photosynthesis.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
