Comparative sequence analysis on the 18S rRNA gene of Aspergillus oryzae, A. sojae, A. flavus, A. parasiticus, A. niger, A. awamori and A. tamarii.

The molds Aspergillus oryzae, A. awamori and A. niger are widely used in the food industry in Japan.On the other hand, A. oryzae, A. flavus and A. parasiticus are very closely related species of the A. flavus group (12).Many isolates of A. flavus and A. parasiticus produce the carcinogenic secondary metabolites, aflatoxins.Therefore, many taxonomical studies on these species have been carried out (3,10,12).Recently, the applicability of molecular biological techniques for bacterial classification such as DNA base composition, DNA homology and sequence comparison of 16S ribosomal RNA (rRNA) is now well accepted (5,16).The sequence comparison of small subunit (16S-like) rRNAs (or rRNA genes) can provide a means for analyzing phylogenetic relationships (18).Chang et al. (1) have used partial sequence comparisons of 18S rRNA comprising 558 nucleotides to determine the evolutionary affinities among eleven species of Aspergillus and associated teleomorphs.Dupont et al. (2) analyzed the 5' end of the 28S-like rRNA molecule (about 130 nucleotides) and constructed a phylogenetic tree computed from the number of nucleotide differences.Recently, a direct sequencing method of rRNA gene (rDNA) using the polymerase chain reaction (PCR) has been developed (17).This study was undertaken to sequence the 18S rRNA genes of A. oryzae, A. awamori and their related species using a direct PCR sequencing method and to get information on phylogenetic relationships among these species.