Comparative Genome Hybridization Reveals Few Genetic Differences between Aspergillus flavus and A. oryzae

Aspergillus flavus and A. oryzae represent two unique species predicted to have spent centuries in vastly different environments. A. flavus is an important opportunistic plant pathogen known for contaminating crops with the carcinogenic mycotoxin, aflatoxin and A. oryzae is a domesticated fungus used in food fermentations. Remarkably, the genomes of these two species are still nearly identical. We have used the recently sequenced genomes of A. oryzae RIB40 and A. flavus NRRL3357 along with array based comparative genome hybridization (CGH) as a tool to compare genomes across several strains of these two species. A comparison of three strains from each species by CGH revealed only 42 and 129 genes unique to A. flavus and A. oryzae, respectively. Further, only 709 genes were identified as being polymorphic between the species. Despite the high degree of similarity between these two species, correlation analysis among all data from the CGH arrays for all strains used in this study reveals a species split. However, this view of species demarcation becomes muddled when focused on only those genes for secondary metabolism. CGH comparison between 3 strains of A. flavus and 3 strains of A. oryzae, analyzed at the probe level