A Polyphasic Approach to Compare the Genomic Profiles of Aflatoxigenic and Non-Aflatoxigenic Isolates of Aspergillus Section Flavi

Abstract

<p>Aflatoxins (AF) are highly toxic compounds produced by Aspergillus section Flavi. They<br />spoil food crops and present a serious global health hazard to humans and livestock. The aim of<br />this study was to examine the phylogenetic relationships among aflatoxigenic and non-aflatoxigenic<br />Aspergillus isolates. A polyphasic approach combining phylogenetic, sequence, and toxin analyses was<br />applied to 40 Aspergillus section Flavi isolates collected from eight countries around the world (USA,<br />Philippines, Egypt, India, Australia, Indonesia, China, and Uganda). This allows one to pinpoint the<br />key genomic features that distinguish AF producing and non-producing isolates. Based on molecular<br />identification, 32 (80%) were identified as A. flavus, three (7.5%) as A. parasiticus, three (7.5%) as<br />A. nomius and one (2.5%) as A. tamarii. Toxin analysis showed that 22 (55%) Aspergillus isolates<br />were aflatoxigenic. The majority of the toxic isolates (62.5%) originated from Egypt. The highest<br />aflatoxin production potential was observed in an A. nomius isolate which is originally isolated<br />from the Philippines. DNA-based molecular markers such as random amplified polymorphic DNA<br />(RAPD) and inter-simple sequence repeats (ISSR) were used to evaluate the genetic diversity and<br />phylogenetic relationships among these 40 Aspergillus isolates, which were originally selected from<br />80 isolates. The percentage of polymorphic bands in three RAPD and three ISSR primers was 81.9%<br />and 79.37%, respectively. Analysis of molecular variance showed significant diversity within the<br />populations, 92% for RAPD and 85% for ISSR primers. The average of Polymorphism Information<br />Content (PIC), Marker Index (MI), Nei’s gene diversity (H) and Shannon’s diversity index (I) in ISSR<br />markers are higher than those in RAPD markers. Based on banding patterns and gene diversities<br />values, we observed that the ISSR-PCR provides clearer data and is more successful in genetic<br />diversity analyses than RAPD-PCR. Dendrograms generated from UPGMA (Unweighted Pair Group<br />Method with Arithmetic Mean) cluster analyses for RAPD and ISSR markers were related to the<br />geographic origin.<br /></p>