Geosiphon
Encyclopedia
Geosiphon is a genus
of fungi in the Geosiphonaceae Family
. 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.
. The Geosiphon-Nostoc
symbiosis, as by modern definitions, is not a lichen
, since it is an intracellular association. Also, by functional and evolutionary implications it is more comparable to the arbuscular mycorrhiza
symbioses than to lichens.
The Geosiphon-Nostoc
symbiosis is the only known fungal endosymbiosis with cyanobacteria and is characterised by a "siphonal bladder" that is made of a swollen fungal hypha, 0.5–2 mm in size and growing on the soil surface. The upper 2/3 of the "bladder" contains the Nostoc filament
s and Nostoc heterocyst
s, the lower 1/3 is filled with lipid
droplets.
s are 250 micrometre
s in diameter, formed at the end of one hypha
, or intercalarly (within a hyphae) and resemble those of members of the Glomeromycota.
active, and are also capable of fixing nitrogen
from the atmosphere. The walls of the bladder have a small pore radius (approximately 0.5 nm), which make it act as an osmotic barrier. This limits the free exchange of nutrients (like sugars) with the environment and increases the need to derive these carbon sources from internal sources. It has been suggested that the organization of the symbiotic interface between the fungus and Nostoc in G. pyriforme is homologous to the symbiotic interface between plant and fungus in arbuscular mycorrhiza in terms of thickness, chitin content, and ultrastructure of layers. G. pyriformis however, is not known to form arbuscular mycorrhiza.
The bladder structure may be considered to be equivalent to a symbiosome, a term used to describe a similar specialized membrane in plants that forms a structural and functional interface between the host and its symbiotic bacterial counterpart. The symbiosome may be divided into three functional areas:
The space between the symbiosome membrane and the Nostoc cell wall contains a 30–40 nm thick layer of carbohydrate material such as mannose
, fucose
, GalNAc, sialic acid
, and galactose
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of fungi in the Geosiphonaceae Family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
. The genus is monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
, 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
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
, 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
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
with endosymbiotic cyanobacteria.
Life cycle
Geosiphon pyriformis is known for being the symbiont of NostocNostoc
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...
. The Geosiphon-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...
symbiosis, as by modern definitions, is not a lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
, since it is an intracellular association. Also, by functional and evolutionary implications it is more comparable to the arbuscular mycorrhiza
Arbuscular mycorrhiza
An arbuscular mycorrhiza is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant....
symbioses than to lichens.
The Geosiphon-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...
symbiosis is the only known fungal endosymbiosis with cyanobacteria and is characterised by a "siphonal bladder" that is made of a swollen fungal hypha, 0.5–2 mm in size and growing on the soil surface. The upper 2/3 of the "bladder" contains the Nostoc filament
Filament
-In physics and electrical engineering:* An electrical filament used to emit light in an Incandescent light bulb* Similarly, a thin heating element* Current filament* Filament propagation, diffractionless propagation of a light beam...
s and Nostoc heterocyst
Heterocyst
Heterocysts are specialized nitrogen-fixing cells formed by some filamentous cyanobacteria, such as Nostoc punctiforme, Cylindrospermum stagnale and Anabaena sphaerica, during nitrogen starvation. They fix nitrogen from dinitrogen in the air using the enzyme nitrogenase, in order to provide the...
s, the lower 1/3 is filled with lipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
droplets.
Reproduction
The fungal sporeSpore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s are 250 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s in diameter, formed at the end of one hypha
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
, or intercalarly (within a hyphae) and resemble those of members of the Glomeromycota.
Somatic structure
Geosiphon has a specialised bladder used to harbour cyanobacteria, usually Nostoc punctiforme, although other Nostoc species are known to be incorporated by the fungus. Geosiphon bladders are photosyntheticallyPhotosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
active, and are also capable of fixing nitrogen
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...
from the atmosphere. The walls of the bladder have a small pore radius (approximately 0.5 nm), which make it act as an osmotic barrier. This limits the free exchange of nutrients (like sugars) with the environment and increases the need to derive these carbon sources from internal sources. It has been suggested that the organization of the symbiotic interface between the fungus and Nostoc in G. pyriforme is homologous to the symbiotic interface between plant and fungus in arbuscular mycorrhiza in terms of thickness, chitin content, and ultrastructure of layers. G. pyriformis however, is not known to form arbuscular mycorrhiza.
The bladder structure may be considered to be equivalent to a symbiosome, a term used to describe a similar specialized membrane in plants that forms a structural and functional interface between the host and its symbiotic bacterial counterpart. The symbiosome may be divided into three functional areas:
- the symbiosome membrane forms the border of the symbiosome. It is thought to be formed from the plasma membrane of the fungus by invaginationInvaginationInvagination means to fold inward or to sheath. In biology, this can refer to a number of processes.* Invagination is the morphogenetic processes by which an embryo takes form, and is the initial step of gastrulation, the massive reorganization of the embryo from a simple spherical ball of cells,...
during the uptake of the symbiont. - the symbiosome space, located between the symbiosome membrane and the endosymbiotic Nostoc cyanobacteria.
- the area containing the cyanobacteria.
The space between the symbiosome membrane and the Nostoc cell wall contains a 30–40 nm thick layer of carbohydrate material such as mannose
Mannose
Mannose is a sugar monomer of the aldohexose series of carbohydrates. Mannose is a C-2 epimer of glucose. It is not part of human metabolism, but is a component of microbial cell walls, and is therefore a target of the immune system and also of antibiotics....
, fucose
Fucose
Fucose is a hexose deoxy sugar with the chemical formula C6H12O5. It is found on N-linked glycans on the mammalian, insect and plant cell surface, and is the fundamental sub-unit of the fucoidan polysaccharide...
, GalNAc, sialic acid
Sialic acid
Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a monosaccharide with a nine-carbon backbone. It is also the name for the most common member of this group, N-acetylneuraminic acid...
, and galactose
Galactose
Galactose , sometimes abbreviated Gal, is a type of sugar that is less sweet than glucose. It is a C-4 epimer of glucose....
.
External links
- Geosiphon at Index FungorumIndex FungorumIndex Fungorum, an international project to index all formal names in the Fungi Kingdom. Somewhat comparable to the IPNI, but with more contributing institutions....
- The Geosiphon pyriformis symbiosis - fungus 'eats' cyanobacterium Schuessler lab
- Glomeromycota phylogeny