Rhizopus

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Rhizopus: a simple guide

What it is
Rhizopus is a group (genus) of common fungi. They live on decaying plant and animal matter and can be saprophytic (feeding on dead material) or, in some cases, opportunistic parasites in humans. They’re found in many everyday places, such as spoiled fruits and vegetables, jellies, syrups, leather, bread, peanuts, and tobacco. Some Rhizopus species can cause a serious illness in people with weak immune systems, called mucormycosis.

What they look like and how they reproduce
- Rhizopus fungi grow as thread-like filaments called hyphae. These hyphae are typically coenocytic, meaning they lack cross-walls.
- They reproduce in two ways:
- Asexual reproduction: spores form inside round structures called sporangia on tall stalks (sporangiophores).
- Sexual reproduction: two compatible fungal partners fuse to form a dark zygospore.
- Rhizopus often grows with root-like structures called rhizoids at the base of the hyphae.

Where they’re found and what they do
- They appear on a wide range of organic matter, especially ripe fruit and vegetables, jellies, syrups, bread, and other foods.
- They help break down and recycle nutrients in the environment, and some species can inhibit the growth of other fungi that produce toxins.

Important species and uses
- Rhizopus oligosporus: used in the fermentation of tempeh (a soy product).
- Rhizopus oryzae: used in making alcoholic beverages in parts of Asia and Africa.
- Rhizopus stolonifer: known as black bread mold; can rot fruits and vegetables but is also used industrially to produce fumaric acid and cortisone.
- Other Rhizopus species can cause soft rot in crops like sweet potatoes and Narcissus flowers.

Ecology and health notes
- Rhizopus plays a role in soil health and nutrient cycling.
- Some strains can increase the nutritional value of feed, and certain studies suggest potential protective effects in animals, such as reduced colon cancer risk in rats or helping piglets resist certain infections.
- Some species act as human pathogens, especially in people with weakened immune systems, highlighting the need for safe handling of moldy foods and medical awareness.

Phylogeny at a glance
- Rhizopus oryzae shows a heterothallic mating system (different mating types) and has a notably large genome with evidence of genome duplication in some species.