Glomus (fungus)

Glomus is a genus of arbuscular mycorrhizal fungus. All of the species in this genus live in mutualistic symbiotic relationships with plant roots. It is a very diverse genus, with ca. 90 species described.

Classification
Glomus is the only genus in the family Glomeraceae. Members of the genus can be distinguished from other members of suborder Glomineae by their darkly-staining arbuscules, multiple spore walls, and lack of a "germination orb" from which the spores germinate. Glomineae are placed in the division Glomeromycota, which includes all of the arbuscular mycorrhizal fungi. Some members of the genus were originally described as Sclerocystis species, but this genus has been entirely transferred to Glomus.

Glomus is likely related to the fossil fungus Glomites, discovered in the Rhynie chert deposits from the Early Devonian (400 million years ago).

Ecology
All members of Glomus exhibit obligate mutualistic relationships with plant roots. They cannot be cultured in the laboratory in the absence of a plant host. Glomus species are found in nearly all terrestrial habitats, including deserts, tropical forests, and tundra.

Arbuscular mycorrhizal fungi provide numerous benefits to their plant hosts, including improved nutrient uptake, drought resistance, and disease resistance.

Life cycle
Glomus species are entirely asexual. Spores are produced at the tips of hyphae either within the host root or outside the root in the soil. Thought to be chlamydospores, these spores germinate and the germination tube that is produced grows through the soil until it comes into contact with roots. The fungus then penetrates the root and grows between root cells, or it may penetrate the cell wall and grow within root cells.

Once inside the root, the fungus forms arbuscules, which are highly branched hyphal structures that serve as sites of nutrient exchange with the plant. It may also form vesicles, which function as food storage organs.

Uses
Several species of Glomus, including G. aggregatum, are cultured and sold as mycorrhizal inoculant for agricultural soils.