Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 9/11/1999
Publication Date: N/A
Technical Abstract: A new aflatoxin producing species of Aspergillus, A. bombycis, was discovered during isolation of fungi from insect frass collected in silkworm rearing houses in central Japan. The new species bears a close resemblance to A. nomius. A. bombycis produces B and G aflatoxins but is distinguished from A. nomius by different growth rates at both 37 and 42 degrees C and by differences in the nucleotide sequences of the species in the ribosomal DNA. Aspergillus bombycis is known from four isolates collected over a period of 10 years at several silkworm rearing houses in Japan. DNA sequence analysis was performed to determine whether the distinctions seen in temperature dependent growth rate were truly species differences. Ribosomal DNA sequences from nuclear genes (ITS1&2, 5.8S rDNA, and 28S rDNA) and mitochondrial genes (18S like rDNA), beta tubulin, and norsolorinic acid reductase (NOR) were sequenced and analyzed using maximum parsimony. In the most parsimonious tree Aspergillus bombycis is a sister species of A. nomius, and these two species form a clade. All of the sequenced genes show A. nomius and A. bombycis to have the same phylogenetic relationship. Other aflatoxigenic and non-aflatoxigenic species from Aspergillus section Flavi occur on a sister branch of the phylogenetic tree that contains the common aflatoxin producing species A. flavus and A. parasiticus. Mycotoxin production information is included on the nucleotide sequence based tree. The parsimony principle suggests that the most recent common ancestor of species in section Flavi had aflatoxin producing ability and that the several non-aflatoxin producing species arrived at that condition by loss of synthetic ability.