Sequence breakpoints in the aXatoxin biosynthesis gene cluster and Xanking regions in nonaXatoxigenic Aspergillus Xavus isolates

Aspergillus Xavus populations are genetically diverse. Isolates that produce either, neither, or both aXatoxins and cyclopiazonic acid (CPA) are present in the Weld. We investigated defects in the aXatoxin gene cluster in 38 nonaXatoxigenic A. Xavus isolates collected from southern United States. PCR assays using aXatoxin-gene-speciWc primers grouped these isolates into eight (A–H) deletion patterns. Patterns C, E, G, and H, which contain 740 kb deletions, were examined for their sequence breakpoints. Pattern C has one breakpoint in the cypA 3 untranslated region (UTR) and another in the verA coding region. Pattern E has a breakpoint in the amdA coding region and another in the ver1 5 UTR. Pattern G contains a deletion identical to the one found in pattern C and has another deletion that extends from the cypA coding region to one end of the chromosome as suggested by the presence of telomeric sequence repeats, CCCTAATGTTGA. Pattern H has a deletion of the entire aXatoxin gene cluster from the hexA coding region in the sugar utilization gene cluster to the telomeric region. Thus, deletions in the aXatoxin gene cluster among A. Xavus isolates are not rare, and the patterns appear to be diverse. Genetic drift may be a driving force that is responsible for the loss of the entire aXatoxin gene cluster in nonaXatoxigenic A. Xavus isolates when aXatoxins have lost their adaptive value in nature. Published by Elsevier Inc.