Genus/species: Rhizopus stolonifer (Rhizopus nigricans)
Classification: Zygomycete
Morphology:
- Cell: coenocytic cells in hyphae with septa only present where gametes form
- Colony: Malt agar: whitish/grey fuzzy colonies WL: no colony formation
- Spores: Many haploid sporagiospores are held within the sporangia structure
- Zygote: Diploid, zygospores that are thicker-walled than the haploid spores and are highly resilient to harsh conditions. They are metabolically inert until environmental conditions improve and then they germinate to produce sporangium or hyphae.
- Ascus: Sporangia which are bulbous structures that sprout from the vegetative hyphae and hold the haploid spores.
Physiological Traits:
Uses sugars or starches as growth substrates and breaks them down to produce shorter carbon chains of alcohol and organic acids.
Ecological Traits:
Spores can be found in the air nearly everywhere, but most especially in humid environments. They are also in the soil.
Distinguishing Features:
Rhizopus stolonifer is unique in that it carries out sexual reproduction when its hyphae of different mating types come into contact, producing the resilient zygospores. The structures formed from this fungus is visible with the naked eye and appears first as a cottony white structure and then turns black on the surface.
Role in wine:
The spores of this fungus can be found in vineyards in hot or humid locations, either in the soil or on the berries. If there is breakage of the berry, the spores can invade the flesh of the berry and begin to feed on its sugars. If these moldy grapes are used to make wine, they will produce a lot of ethyl acetate which is a volatile aroma. This is unpleasant, and not wanted in wine.
Sensitivities:
SO2, Ethanol, Heat to some extent, but it will not kill all of the cells, Calcium hypochlorite.
References:
Corison et al. 1979. Must Acetic Acid and Ethyl Acetate as Mold and Rot Indicators in Grapes. AJEV. 30 (2): 130.