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Fungi: Zygomycota

Rhizopus nigricans (a.k.a. Bread Mold)

A. Species Name

  • Rhizopus nigricans

B. Native Enviroment

  • Rhizopus is a cosmopolitan filamentous fungus found in soil, decaying fruit and vegetables, animal feces, and old bread. While Rhizopus spp. are common contaminants, they are also occasional causes of serious (and often fatal) infections in humans. Some species are plant pathogens

C. Characteristics of the Organism

  • Rhizopus rot is a soft rot of harvested or over-ripe stone fruits, such as peaches, nectarines, sweet cherries, and plums. Mold species belonging to the genus Rhizopus cause the rot, which initially appears on the fruit as a fuzzy white mass, called the mycelium.
  • The fungus produces enzymes that deteriorate the tissue, holding the skin to the flesh of the fruit.
  • Later, the fruit turns dark gray to black as the fungus begins to develop spherical sporangia. The sporangia can reproduce asexually via mitospores (or sporangiospores, diploid or 2N), or sexually.
  • Each sporangium, the fruiting structure, produces desiccation- and cold-resistant thick-walled zygospores (diploid or 2N) via conjugation of the isogametes (haploid or N) in the gametangia when growing conditions are not favorable.
  • Once released into the air, the spores can infect injured fruit, in both orchards and on kitchen countertops.
  • After infecting a host, such as a slice of bread, the mold (R. nigricans) will form mature zygospores within four or five days.

D. Adaptaions to The Enviroment

  • R. stolonifer is a species that commonly affects damaged fruit in household kitchens, although uninjured fruits are not susceptible to the disease.
  • Rhizopus has probably evolved to be especially effective against common materials in its enviroment. It can easily infect bread, becuase it is so common all over the world, and is thus a good food source.

E. Ecological and Medical Roles

  • decomposers (saprobes) - absorb nutrients from dead organic material, including:
    • wood
    • non-living organic material (dead plants and animals, feces)
    • man-made products (paper, leather, cloth, )
  • Decomposition is a critical ecological role! Fungi return staggering amounts of CO2 to the atmosphere and return nutrients to the soil.Without fungi and bacteria, critical nutrients would be unavailable - 'locked up' in dead plant and animal matter.
  • Remember - mold is good! ('Mold' is not a taxonomic term. It merely refers to the rapid, asexual growth of many types of fungi).
  • mutualistic symbionts - almost all plants depend on fungi to increase surface area for water and mineral absorption from the soil. These associations between plant roots and fungi are called mycorrhizae.
  • The fungus benefits by obtaining organic nutrients synthesized by the plant. Mycorrhizae are critical to both natural and agricultural ecosystems and may have contributed to original colonization of plants onto land by enabling them to thrive, even in nutrient-poor soils.
  • parasites - absorb nutrients from other living cells.
    • some are serious plant pathogens
    • some are animal pathogens

F. A PIcture or Sample of the Organism

Three Images of Rhizobus

rhizopus rhizopus rhizopus

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