Rhizopus oryzae
Rhizopus oryzae | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Fungi |
Division: | Mucoromycota |
Order: | Mucorales |
Family: | Mucoraceae |
Genus: | Rhizopus |
Species: | R. oryzae
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Binomial name | |
Rhizopus oryzae Went & H.C. Prinsen Geerligs, (1895)
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Synonyms | |
Rhizopus arrhizus A. Fisch., (1892) |
Rhizopus oryzae is a filamentous
History and taxonomy
Rhizopus oryzae was discovered by Frits Went and Hendrik Coenraad Prinsen Geerligs in 1895.[1] The genus Rhizopus (family Mucoraceae) was erected in 1821 by the German mycologist, Christian Gottfried Ehrenberg[2] to accommodate Mucor stolonifer and Rhizopus nigricans as distinct from the genus Mucor.[3] The genus Rhizopus is characterized by having stolons, rhizoids, sporangiophores sprouting from the points of which rhizoids were attached, globose sporangia with columellae, striated sporangiospores.[3] In the mid 1960s, researchers divided the genus based on temperature tolerance. Numerical methods were later used in the early 1970s where researchers arrived at similar conclusions. R. oryzae was relegated to a distinct section because it grew well at 37 °C but failed to grow at 45 °C.[4] In the past, strains were identified through isolating active components of the species that were commonly found in food and alcoholic drinks in Indonesia, China, and Japan.[4] There are approximately 30 synonyms, the most common being R. arrhizus.[5] Scholer popularized R. oryzae because he thought R. arrhizus represented an extreme form of R. oryzae.[4]
Growth and morphology
Rhizopus oryzae grows quickly in optimal temperatures, at 1.6 mm per hour (nearly 0.5 μm per second - enough to be able to directly visualize hyphal elongation in real-time under the microscope).[1] R. oryzae can grow in temperature of 7 °C to 44 °C and the optimum growth temperature is 37 °C.[1][6] There is very poor growth from 10 °C to 15 °C[3] and negligible growth at 45 °C.[2][4] There is substantial growth in media containing 1% NaCl, very poor growth at 3% NaCl, and none at 5% NaCl. R. oryzae favors slightly acidic media. Good growth is observed at a pH of 6.8; in the range of 7.7-8.1, there is very poor growth.[3] Most amino acids—with the exception of L-valine—promote R. oryzae growth, with L-tryptophan and L-tyrosine being the most effective. It also grows well on mineral nitrogen sources, except nitrate, and can utilize urea.[7]
Rhizopus oryzae has variable sporangiosphores. They can be straight or curved, swollen or branched, and the walls can be smooth or slightly rough. The colour of sporangiosphores range from pale brown to brown. Sporangiosphores grow between 210-2500 μm in length and 5-18 μm in diameter. The
Habitat and ecology
Rhizopus oryzae can be found in various soils across the world. For example, it has been found in India, Pakistan, New Guinea, Taiwan, Central America, Peru, Argentina, Namibia, South Africa, Iraq, Somalia, Egypt, Libya, Tunisia, Israel, Turkey, Spain, Italy, Hungary, Czech Republic, Slovakia, Germany, Ukraine, British Isles, and the USA. The soils where R. oryzae has been isolated are varied ranging from grassland, cultivated soils under lupin, corn, wheat, groundnuts, other legumes, sugar canes, rice, citrus plantations, steppe type vegetation, alkaline soils, salt-marshes, farm manure soils, to sewage filled soils. The pH of the soils where the species has been isolated typically range from 6.3 to 7.2.[7]
Rhizopus oryzae is often identified as R. arrhizus when isolated from foods. It is found in rotting fruits and vegetables where it is often called R. stolonifer. Unlike the other species such as R. stolonifer, R. oryzae is common in tropical conditions. In East Asia, it is common in peanuts. For instance, there was 21% isolation from peanut kernels from Indonesia.[1] It is present in maize, beans, sorghum, and cowpeas, pecans, hazelnuts, pistachios, wheat, barley, potatoes, sapodillas, and various other tropical foods.[1] Maize meal on which isolates of R. oryzae had been grown was found to be toxic to ducklings and rats, causing growth depression.[4]
Pathogenicity
Rhizopus oryzae is one of the most common causes of a disease known as mucormycosis, characterized by growing hyphae within and surrounding blood vessels. The causal agents of mucormycosis may also produce toxins like agroclavine which is toxic to humans, sheep and cattle.[7] This infection usually occurs in immunocompromised individuals but is rare.[9][10] Common risk factors associated with primary cutaneous mucormycosis is ketoacidosis, neutropenia, acute lymphobloastic leukemia, lymphomas, systemic steroids, chemotherapy, and dialysis. Treatment includes amphotericin B, posaconazole, itraconazole, and fluconazole.[11] The majority of the cases of infection are rhinocerebral infections. At the same time, it has been found in literature that R. oryzae can produce antibiotic activity on some bacteria.[7]
The pathogenicity towards plants is attributed to the presence of large number of carbohydrate digesting enzymes.[citation needed]
Physiology and industrial uses
Rhizopus oryzae is involved in steroid transformations and it produces 4-desmethyl steroids which has been useful in the fermentation industry. The carbon sources does influence the ratio of polar and neutral lipids. The mycelium found in R. oryzae contains lipids and the highest lipid content occurs when grown on fructose. The highest unsaturated fatty acid content is observed at 30 °C and lowest at 15 °C. Proteolytic properties have been observed well under the conditions of pH 7 at 35 °C. Pyridozine and thiamine prefer proteinase production. R. oryzae can degrade aflatoxin A1 to isomeric hydroxy compounds and aflatoxin G1 to fluorescent metabolite aflatoxin A1.[7] There are various factors that influence the production of dextro-lactic acids, fumaric acid, and metabolism of R. oryzae. For examples, in 40 °C there is more favorable growth for glucose consumption, however this influenced production of d-lactic acid production negatively. Glucose concentration of 15% is needed for optimal production of d-lactic acid. Fumaric acid production was suppressed in media containing more than 6 grams of NH4NO3 per liter and is favorable to d-lactic acid production.[12]
Rhizopus oryzae is considered GRAS by the FDA and thus recognized as safe to use industrially as it can consume a range of carbon sources.[13] During fermentation. R. oryzae produce amylase, lipase, and protease activity to increase nutrient's ability to use many compounds as an energy and carbon source.[14] Historically, it has been used in fermentation, specifically to ferment soybean and create tempeh in Malaysia and Indonesia.[15] Using the same methods to create traditional tempeh, R. oryzae can be inoculated in other cooked legumes such as peas, beans, and fava beans. Similarly in tempeh making, there is an initial bacterial fermentation in legumes when they are soaked for a while before being cooked. Fermentation incubation lasts for 48 hours at 33 °C. After incubation, mycelium can be observed between the legumes creating a larger, uniform product. Overall, fruits, grains, nuts, and legumes mold-fermentation with R. oryzae produces sensory changes in foods such as creating acidity, sweetness and bitterness. R. oryzae can produce lactate from glucose at high levels, which is used as a food additive and can also degrade plastics.[16] In enzyme-modified cheese products, R. oryzae provides microbial enzymes where milk fat and proteins are broken down to create powder and paste forms of cheese. Specifically, it breaks down cheese curds and acid casein.[17]
Among finding
References
- ^ ISBN 978-0834213067.
- ^ ISBN 978-9070351267.
- ^ ISSN 1349-8037.
- ^ a b c d e Schipper, M.A.A (1984). "A revision of the genus Rhizopus. I. The Rh. stolonifer-group and Rh. oryzae". Studies in Mycology. 25: 1–19.
- ^ Fischer, A (1892). Rabenhorst's Kryptogamen-Flora, Pilze - Phycomycetes (2 ed.). Eduard Kummer, Leipzig.
- ^ )
- ^ ISBN 978-0122204012.
- PMID 21151560.
- PMID 25830548.
- PMID 15664916.
- S2CID 33088979.
- ^ Lockwood, L.B. (1963). "The physiology of rhizopus oryzae".
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(help) - PMID 21945206.
- .
- PMID 28651077.
- ISBN 9781855739666.
- ISBN 9781845698119.
- PMID 20850485.