Evolutionary relationships among Aspergillus oryzae and related species based on the sequences of 18S rRNA genes and internal transcribed spacers.

The mold Aspergillus oryzae is widely used in Japan as a koji mold for the fermentation of sake, miso, and soy sauce and belongs to the genus Aspergillus section Flavi (Gams et al., 1985), which includes A. flavus, A. sojae, A. tamarii, A. parasiticus, and A. nomius.Aspergillus sojae is also used as a koji mold for soy sauce fermentation.On the other hand, A. flavus, A. parasiticus, and A. nomius are known to commonly infect cereal grains and peanuts; it is also kwown that many of their isolates produce aflatoxins, the carcinogenic secondary metabolites.Many taxonomical studies on these species have been carried out (Gams et al., 1985;Klich and Pitt, 1988;Murakami, 1971;Raper and Fennell, 1965).Kurtzman et al. (1986) investigated the DNA relatedness among A. flavus, A. oryzae, A. parasiticus, and A. sojae.They showed that all four species had high (69-100%) nuclear DNA homology and similar genomic size.On the basis of these genotypic characters, they proposed that the four taxa represented a single species (Kurtzman et al., 1986).Chemotaxonomic approaches have also been used by Kuraishi et al. (1990) andYamatoya et al. (1990).The latter attempted to evaluate the conflicting concepts of speciation in Aspergillus section Flavi by using combinations of chemotaxonomic criteria such as electrophoretic Evolutionary relationships among Aspergillus oryzae and related species based on the sequences of 18S rRNA genes and internal transcribed spacers