Rhizopus stolonifer

This fungus was first discovered by the German scientist Christian Gottfried Ehrenberg in 1818 as Rhizopus nigricans. The name was changed in 1902 to Rhizopus stolonifer by the French mycologist J. P. Vuillemin. == Habitat and ecology ==

Rhizopus stolonifer has a cosmopolitan distribution and is found on all types of mouldy materials. It is often one of the first molds to appear on stale bread. It can exist in the soil as well as in the air. A variety of natural substrata are colonized by this species because R. stolonifer can tolerate broad variations in the concentration of essential nutrients and can use carbon and nitrogen combined in diverse forms. In the laboratory, this fungus grows well on different media, including those that contain ammonium salts or amino compounds. However, R. stolonifer will not grow on Czapek's agar because it cannot utilize nitrogen in the form of nitrate. Rhizopus lives in hyphae and matured spores. == Growth and physiology ==

This species is known as a saprotroph and plays an important role in the early colonization of substrata in soil. Nonetheless, it can also behave as a parasite of plant tissues causing a rot of vegetables and fruits. Sporangiophores of R. stolonifer can be up to 2.5 mm long and about 20 μm in diameter. The spores are shaped differently depending on the available nutrients. They can be ovate, polygonal or angular. The optimal temperature for growth varies between 25 and 30 °C. The thermal death point, which is defined as the lowest temperature that can kill all cells in ten minutes, is 60 °C. Rhizopus stolonifer can grow in acidic environments with a pH of as low as 2.2. The pH range can vary from 2.2 to 9.6. Ultraviolet irradiation can delay spore germination. == Reproduction ==

Rhizopus stolonifer can reproduce asexually and sexually. It is a heterothallic species. Sexual reproduction occurs when compatible haploid mating types in the form of hyphae make contact with each other, producing diploid zygospores. The sporangiophore contains both '+' and '−' mating type strains in the form of sporangiospores. Meiosis is delayed until the germination of the zygospores. The gametogenia often differ in size, regardless of mating type. This difference in size is not due to sex but presumably due to nutrition. == Disease and prevention ==

The disease caused by this fungus occurs mainly on ripe fruits, such as strawberries, melon and peach, which are more susceptible to wounds and have a higher sugar content. After a couple of days, the infected fruits become soft and release juices with an acidic odour. The disease can also affect other adjacent healthy fruits when distributed by wind or insect activity. The action of smelling spoiled food may be a source of inhalation exposure to the mold. == Importance ==

Rhizopus stolonifer is important economically as an agent of post-harvest storage decay. While Saccharomyces cerevisiae is the most important source of industrial alcohol, R. stolonifer and other species of Rhizopus also produce ethyl alcohol which is the most important fermentation product. Rhizopus stolonifer is also used commercially to manufacture fumaric acid and lactic acid of high purity. The presence of zinc reduces the amount of fumaric acid produced by the fungus. == References ==