Aspergillus flavus resident in Kenya: High genetic diversity in an ancient population primarily shaped by clonal reproduction and mutation-driven evolution.

Md-Sajedul Islam,Charity Mutegi,Peter J. Cotty,Kenneth A. Callicott,Ranajit Bandyopadhyay

doi:10.1016/j.funeco.2018.05.012

Abstract

Aspergillus flavus has long been considered to be an asexual species. Although a sexual stage was recently reported for this species from in vitro studies, the amount of recombination ongoing in natural populations and the genetic distance across which meiosis occurs is largely unknown. In the current study, genetic diversity, reproduction and evolution of natural A. flavus populations endemic to Kenya were examined. A total of 2744 isolates recovered from 629 maize-field soils across southern Kenya in two consecutive seasons were characterized at 17 SSR loci, revealing high genetic diversity (9-72 alleles/locus and 2140 haplotypes). Clonal reproduction and persistence of clonal lineages predominated, with many identical haplotypes occurring in multiple soil samples and both seasons. Genetic analyses predicted three distinct lineages with linkage disequilibrium and evolutionary relationships among haplotypes within each lineage suggesting mutation-driven evolution followed by clonal reproduction. Low genetic differentiation among adjacent communities reflected frequent short distance dispersal.

Highlights

Aspergillus section Flavi includes several species of closely related fungi that frequently contaminate crops with aflatoxins
A. flavus readily disperses through the air (Bock et al, 2004) it survives in soil as conidia, sclerotia and colonized crop material (Diener et al, 1987; Horn, 2003), with soil reservoirs serving to initiate new cycles of population increase (Jaime-Garcia and Cotty, 2004; Cotty et al, 2008)
Simple sequence repeat (SSR) analyses in the present study suggest that natural populations of A. flavus in Kenya are largely evolving in the absence of meiosis through a clonal process

Summary

Introduction

Aspergillus section Flavi includes several species of closely related fungi that frequently contaminate crops with aflatoxins. Aspergillus flavus is an important member of this section which infects various food and feed crops, including maize, peanut, cottonseed, and tree nuts, both prior to harvest and during storage. This fungal infection often results in contamination of the crop with aflatoxins, highly toxic and carcinogenic polyketide fungal metabolites (Eaton and Gallagher, 1994; Sweeney and Dobson, 1998). Aflatoxin contaminates 25% of world food crops, and 4.5 billion people in the developing countries, especially in Africa and Asia, are chronically exposed to aflatoxins in their daily diets (Williams et al, 2004). The most effective method for preventing aflatoxins is a type of biocontrol that uses atoxigenic genotypes of A. flavus to alter fungal communities associated with crops so that aflatoxin producers are less common and the potential for contamination is reduced

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Discussion

Conclusion