Aspergillus affinis sp. nov., a novel ochratoxin A-producing Aspergillus species (section Circumdati) isolated from decomposing leaves

Abstract

Two ochratoxin A (OTA)-producing Aspergillus isolates, recently collected from submerged riparian decomposing leaves in Italy, were found to have a similar morphology to Aspergillus cretensis (subgenus Circumdati, section Circumdati). However, marked differences emerged between these two novel isolates and A. cretensis as the former displayed different colony features and had larger vesicles, metulae, phialides and conidia, as well as a distinct sclerotial form and size. In order to determine the taxonomic status and to infer the evolutionary relationships of these two morphologically identical isolates, a molecular phylogenetic analysis was performed on all the officially recognized lineages in the section Circumdati. The DNA sequences and the deduced amino acid residues from the nuclear loci were analysed. Both rRNA and protein coding genes were assessed, which are widely used to differentiate taxa belonging to genus Aspergillus at various evolutionary levels. The 5.8S rDNA gene and internal transcribed spacers (ITS), the D1/D2 domains of the 28S rDNA gene, a region of the tubulin beta chain gene (benA) and part of the calmodulin gene (cmd) were amplified by PCR and then sequenced. The analysis of the rRNA regions and of the benA and cmd sequence data indicated that the two isogenic isolates belonged to a genetically distinct OTA-producing species of the genus Aspergillus. The isolates are proposed as representing a novel species, Aspergillus affinis sp. nov., with the type strain ATCC MYA-4773T ( = CBS 129190 = 417). Phylogenetically, A. affinis sp. nov. appeared to be very closely related to A. cretensis, from which it could be distinguished by means of a morphological trait analysis.