A Polyphasic Approach to Compare the Genomic Profiles of Aflatoxigenic and Non-Aflatoxigenic Isolates of Aspergillus
Asmaa Abbas1,2, Taha Hussien1,3, Tapani Yli-Mattila1
1Department of Biochemistry, University of Turku, FI-20014 Turku, Finland.
Abstract:
Aflatoxins (AF) are highly toxic compounds produced by Aspergillus section Flavi. They spoil food crops and present a serious global health hazard to humans and livestock. The aim of this study was to examine the phylogenetic relationships among aflatoxigenic and non-aflatoxigenic Aspergillus isolates. A polyphasic approach combining phylogenetic, sequence, and toxin analyses was applied to 40 Aspergillus section Flavi isolates collected from eight countries around the world (USA, Philippines, Egypt, India, Australia, Indonesia, China, and Uganda). This allows one to pinpoint the key genomic features that distinguish AF producing and non-producing isolates. Based on molecular identification, 32 (80%) were identified as A. flavus, three (7.5%) as A. parasiticus, three (7.5%) as A. nomius and one (2.5%) as A. tamarii. Toxin analysis showed that 22 (55%) Aspergillus isolates were aflatoxigenic. The majority of the toxic isolates (62.5%) originated from Egypt. The highest aflatoxin production potential was observed in an A. nomius isolate which is originally isolated from the Philippines. DNA-based molecular markers such as random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR) were used to evaluate the genetic diversity and phylogenetic relationships among these 40 Aspergillus isolates, which were originally selected from 80 isolates. The percentage of polymorphic bands in three RAPD and three ISSR primers was 81.9% and 79.37%, respectively. Analysis of molecular variance showed significant diversity within the populations, 92% for RAPD and 85% for ISSR primers. The average of Polymorphism Information Content (PIC), Marker Index (MI), Nei's gene diversity (H) and Shannon's diversity index (I) in ISSR markers are higher than those in RAPD markers. Based on banding patterns and gene diversities values, we observed that the ISSR-PCR provides clearer data and is more successful in genetic diversity analyses than RAPD-PCR. Dendrograms generated from UPGMA (Unweighted Pair Group Method with Arithmetic Mean) cluster analyses for RAPD and ISSR markers were related to the geographic origin.
Insights
This study investigated aflatoxin-producing Aspergillus species, finding significant genetic diversity and geographical links. Inter-simple sequence repeat (ISSR) markers proved more effective than random amplified polymorphic DNA (RAPD) for analyzing these toxin-producing fungi.
Area of Science:
- Mycology
- Food Science
- Genetics
Background:
- Aflatoxins (AF) are toxic fungal metabolites produced by Aspergillus section Flavi, posing health risks to humans and livestock.
- Contamination of food crops by aflatoxins is a significant global concern.
Purpose of the Study:
- To analyze the phylogenetic relationships between aflatoxigenic and non-aflatoxigenic Aspergillus isolates.
- To identify genomic features distinguishing aflatoxin-producing from non-producing strains.
Main Methods:
- A polyphasic approach combining phylogenetic, sequence, and toxin analyses on 40 Aspergillus section Flavi isolates from eight countries.
- Molecular identification using DNA-based markers: random amplified polymorphic DNA (RAPD) and inter-simple sequence repeats (ISSR).
- Analysis of molecular variance (AMOVA) and dendrogram generation using UPGMA.
Main Results:
- Out of 40 isolates, 22 (55%) were aflatoxigenic, with most originating from Egypt.
- Aspergillus nomius from the Philippines showed the highest aflatoxin production potential.
- ISSR markers demonstrated higher genetic diversity and were more successful than RAPD for phylogenetic analysis.
- Genetic diversity analysis revealed significant variation within populations, with ISSR markers yielding clearer data.
Conclusions:
- Phylogenetic relationships and genetic diversity among Aspergillus isolates are influenced by geographic origin.
- ISSR-PCR is a more effective molecular marker for differentiating Aspergillus species and assessing genetic diversity compared to RAPD-PCR.
- Understanding the genetic basis of aflatoxin production is crucial for developing control strategies.
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