Zygomycetes is a historical informal name for a group of filamentous fungi that produce sexual spores called zygospores. In classical taxonomy these organisms were placed in the phylum Zygomycota, but molecular studies have since divided them into the phyla Mucoromycota and Zoopagomycota. Members of this assemblage share features such as fast-growing, coenocytic hyphae and asexual sporangiospores borne in sporangia.
Morphology and reproduction
Zygomycetes have non-septate (coenocytic) hyphae that form a cottony mycelium. Asexual reproduction occurs when sporangiophores emerge from the hyphae, each terminating in a spherical sporangium containing hundreds of sporangiospores. Upon maturation, the sporangium ruptures to release spores that germinate into new hyphae under suitable conditions. Sexual reproduction is triggered by nutrient limitation and involves fusion of specialized hyphal tips from compatible mating types to form gametangia. The gametangia merge to produce a thick-walled zygosporangium enclosing a single zygospore. This dormant structure undergoes meiosis and eventually germinates, giving rise to a sporangiophore with haploid sporangiospores, completing the life cycle.
Ecology and importance
Most zygomycetous fungi are saprotrophs that decompose dead plant material, dung, and other organic substrates. *Rhizopus stolonifer*, the common black bread mold, colonizes starchy foods and is used industrially to ferment soybeans into tempeh and produce organic acids such as lactic and fumaric acid. *Mucor* species are employed in cheese ripening but can also spoil food. Some genera, including *Rhizomucor*, *Mucor*, and *Lichtheimia*, cause opportunistic infections in humans known as mucormycosis, particularly in immunocompromised patients. Other members like *Pilobolus* eject their sporangia towards light, facilitating dispersal from herbivore dung. Overall, zygomycetes play significant roles in nutrient recycling, food production, and, occasionally, disease.
While the taxonomic placement of zygomycetes has changed, the term remains useful for describing fungi that form zygospores and exhibit coenocytic hyphae. Understanding their morphology and life cycles aids in appreciating their ecological functions and industrial and medical significance.
Related Terms: Zygospore, Sporangiospore, Mucor, Rhizopus, Coenocytic hypha