Geosiphon
Geosiphon pyriformis among phylogenetically arbuscular mycorrhizal fungi to, even though no mycorrhizal symbiosis has been demonstrated for him and is the only type of Geosiphonaceae family. He lives on loamy, nutrient-poor soils in symbiosis with certain strains of blue-green algae Nostoc punctiforme of.
Form, meaning, and distribution
The photosynthetically active symbiotic partner grows in about 1.5 mm long, dark shiny bubbles of the otherwise microscopic fungus. It is the only known symbiosis, grown in the cyanobacteria within the cells of the fungus. Cyanobacteria exist in the form of lichens with fungi in symbiosis. Here, however, the cyanobacteria grow exclusively extracellular. So far, only a few finds for Geosiphon pyriformis are documented. The locations are in Germany and Austria, where the Spessart is the main area of distribution.
Function and mode of origin of the symbiosis with Nostoc
Geosiphon pyriformis is an obligate symbiont, that is, it does not grow outside the symbiosis. The cyanobacteria, however, are facultative symbiotic partners and can free-living increase. Free-living Nostoc strains are taken as filaments from a few cells via endocytosis of the hyphae of the fungus. Then grow from the hyphae to the macroscopic bubble in which multiply the recorded cyanobacteria and form heterocysts for N2 fixation. Nostoc cells only for a certain state, the called primordium was added. This is the transition from the moving propagation phase for fixed life form in the form of Gallertklümpchen the typical Nostoc stock. The recognition of this symbiosis compatible phase is probably based on a lectin - mediated process. The fungus receives from the cyanobacteria, the photosynthetic sugar formed and possibly nitrogen compounds from the heterocysts. For the benefit of Nostoc symbiosis is in sufficient for growth and photosynthesis supply of water, phosphate and CO2.
Symbiosis as an argument for the endosymbiont theory
The fungus is considered to be a witness for the early phylogeny of plants. To him can understand the endosymbiont theory, because he receives free-living cyanobacteria and uses for its own metabolism. According to the endosymbiont theory, the chloroplasts have evolved from a comparable " domestication " of cyanobacteria.
Symbiosis with other organisms
Geosiphon pyriformis lives simultaneously with other organisms in symbiosis: First one other bacterial previously but unidentified endosymbiont is found, which occurs in many different arbuscular mycorrhizal fungi. On the other hand, the fungus continues to grow in the company of hornworts ( Anthoceros and Phaeoceros ) and from the liverwort Blasia pusilla. The fungal hyphae are here associated with the thalli and rhizoids of the accompanying moss plants which also live with Nostoc in symbiosis. The Nostoc strains grow extracellularly in these mosses and are compatible with Geosiphon pyriformis.