| CAS No.: | 9000-92-4 |
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| Color: | White |
| Appearance: | Powder |
| Transport Package: | Paper |
| Specification: | large |
| Trademark: | china |
| Samples: |
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Audited Supplier Aspergillus oryzae plays a pivotal role in Asian food manufacturing, such as saké, shoyu (soy sauce), and miso (soybean paste). For thousands of years, it has been used for making fermented food and beverages. In addition, A. oryzae has been used in the production of industrial enzymes for food processing. A. oryzae is accepted as a microorganism having generally regarded as safe status.
A. oryzae is an aerobic filamentous fungus and belongs to the Aspergillus subgenus Circumdati section Flavi, previously known as the A. flavus group. Aspergillus section Flavi contains industrially important species, such as A. oryzae, as well as agronomically and medically significant fungi, such as A. flavus and A. parasiticus, which produce a potent carcinogenic substance, aflatoxin. Taxonomically, A. oryzae is closely related to A. flavus, A. parasiticus, and A. sojae, which has also been used for shoyu fermentation for a long time. Despite such close relatedness, A. oryzae and A. sojae never produce aflatoxins and are used in fermented food manufacturing. Thus, it is of great importance to differentiate these four species accurately, although recent taxonomical studies on Aspergillus section Flavi have some controversial aspects.
A. oryzae is isolated from soils and plants, particularly rice. A. oryzae is named after its occurrence in nature and cultivation industrially on rice, Oryza sativa. A. oryzae has an optimal growth temperature of 32-36 °C (±1 °C) and is unable to grow above 44 °C. It has an optimal growth pH of 5-6 and can germinate at pH 2-8. It has been reported that A. oryzae could grow in corn flour with a water content of about 16%. It generally can grow on media with a water activity (aw) above 0.8, but it rarely grows below 0.8.
Like most other fungi, A. oryzae grows vegetatively as haploid multinucleate filaments, designated hyphae, or mycelia. Hyphae of A. oryzae extend at the apical tips and multiply by branching, so that the colony covers the surface of the solidified agar medium after several days of incubation. Hyphal growth keeps on going in liquid medium as long as the hyphae are not exposed to air atmosphere. Conidiophore structures, however, which bear asexual reproductive spores called conidia (Figure 1), are produced when hyphae are transferred onto solidified agar medium. When grown on the surface of an agar medium, the colony is initially white because of the vegetative hyphal growth, and then it turns to yellowish green as a large amount of conidia form. In most strains of A. oryzae, the color of fresh culture or conidia is yellowish green, but that of old culture is brown, sometimes green with brown shades. Conidial heads are usually globose to radiate, 100-200 μm in diameter. In A. oryzae, sexual life cycle has not been found as in other industrially important filamentous fungi, such as A. niger and Penicillium chrysogenum. Conidia of A. oryzae are haploid, but multinucleate (conidia have mostly two to four or more nuclei) in contrast to uninucleate conidia of A. nidulans or A. niger. This makes genetic manipulation of A. oryzae more difficult, compared with A. niger. Conidia are large, 5-8 μm in diameter, and spherical to slightly oval. Conidial walls are mostly smooth to finely roughened. Most strains of A. oryzae have only phialides on the vesicles (uniseriate sterigmata), but some contain metulae and phialides (biseriate sterigmata). Stipes of conidiophores are colorless and mostly roughened, to occasionally smooth and less roughened. They are long, in the range 1-5 mm.
Figure 1. Conidiophore structures of A. oryzae.
Because of the difficulties of classical genetic analyses, little was known of the genetics of A. oryzae, or its fine genetic map. Recently, however, by means of pulsed-field gel electrophoresis (PFGE), electrophoretic karyotyping of an A. oryzae strain, RIB40, has been accomplished. A. oryzae chromosomes prepared from protoplasts were separated by PFGE and gave seven ethidium bromide (EtdBr)-stained bands. The sizes of these were estimated roughly as 7.0, 5.2, 5.0, 4.5, 4.0, 3.7, and 2.8 Mbp, in comparison with the chromosome size of Schizosaccharomyces pombe. Of these seven chromosomal bands, the smallest was assumed to be a doublet suggested by the fluorescence intensity of EtdBr stain and the results of Southern blot analyses with 100 random clones isolated from A. oryzae. Consequently, it is likely that A. oryzae has eight chromosomes and the genome size is approximately 35 Mbp. The number of chromosomes is the same as that of A. nidulans and A. niger, and the genome size also is consistent with that of A. nidulans (31 Mbp) and A. niger (36-39 Mbp). In addition, 13 genes - including rDNA of A. oryzae - were hybridized to the chromosomal bands, and at least one gene was assigned to an individual chromosome. The related fungus A. flavus has also been electrophoretically karyotyped and was assumed to have eight chromosomes and an estimated 36 Mbp genome size. When chromosomes derived from genealogically different strains of A. oryzae were separated on PFGE, the results revealed slightly different patterns. This indicated that changes in genome organization such as a chromosomal translocation often have occurred in A. oryzae intraspecifically. Also, this fact means that the electrophoretic karyotype cannot be used to distinguish A. oryzae from A. flavus, although it would be expected to be a promising taxonomic criterion.
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