Molecular characterization of atoxigenic strains for biological control of aflatoxins in Nigeria

Abstract

Aflatoxins are highly toxic carcinogens produced by several species in Aspergillus section Flavi. Strains of A. flavus that do not produce aflatoxins, called atoxigenic strains, have been used commercially in North America as tools for limiting aflatoxin contamination. A similar aflatoxin management strategy is being pursued in Nigeria. In the current study, loci across the 68 kb aflatoxin biosynthesis gene cluster were compared among 18 atoxigenic and two aflatoxin-producing vegetative compatibility groups (VCGs) from Nigeria and an atoxigenic VCG used commercially in North America. Five of the atoxigenic VCGs had large deletions (37-65 kb) extending from the teleomeric side of the aflatoxin biosynthesis cluster. In one VCG (AV0222) the deletion extended through the cluster to the adjacent sugar cluster. The remaining twelve atoxigenic VCGs, including the VCG used for aflatoxin management in North America, contained all the aflatoxin pathway genes, but with defects. Two observations support the long-term persistence of atoxigenicity within A. flavus: first, a comparison of pathway genes revealed more changes in atoxigenic than in aflatoxin-producing isolates relative to the aflatoxin-producing strain NRRL 3357; and second, several non-synonymous changes are unique to atoxigenics. Atoxigenic VCG diversity was assessed with phylogenetic analyses. Although some atoxigenics share relatively recent ancestry, several are more closely related to aflatoxin producers than to other atoxigenics. The current study demonstrates VCGs of A. flavus in West Africa with diverse mechanisms of atoxigenicity and potential value in aflatoxin management programmes.

International agricultural research to reduce food risks: case studies on aflatoxins

“…In 2003, the biocontrol effort moved to Nigeria with continued funding from the German government and in collaboration with USDA-ARS and University of Ibadan. Initially, more than 4200 Aspergillus strains collected from maize and soil samples in Nigeria were tested and approximately 20 atoxigenic genetic groups were selected (Donner et al 2010). The atoxigenic groups were evaluated for growth rate, sporulation, and competitiveness in vitro and in vivo (Atehnkeng et al 2008b).…”

Genetic Analysis of the Aspergillus flavus Vegetative Compatibility Group to Which a Biological Control Agent That Limits Aflatoxin Contamination in U.S. Crops Belongs

“…As more biological control programs to reduce aflatoxin contamination are pursued globally, the strains used as biopesticides should be derived from local fungal populations and should not be based on atoxigenic strains that are not indigenous to the targeted region. Current efforts in Nigeria (73,74) and Kenya, where atoxigenic strains of A. flavus are being developed for commercial applications to maize (17), adhere to the precept of identifying endemic fungi for use in aflatoxin control.…”

Biological control of aflatoxins in Africa: current status and potential challenges in the face of climate change

“…With funding from the German Government, more than 4,200 Aspergillus isolates collected from maize and soil samples in Nigeria in 2003 were subjected to diverse studies that helped to identify 20 atoxigenic VCGs native to the major maize-producing regions of Nigeria (Donner et al, 2010). Representative isolates of the 20 atoxigenic VCGs were evaluated in laboratory experiments for growth rate, reproduction (sporulation), and ability to reduce aflatoxins when challenged with highly toxigenic isolates (Atehnkeng et al, 2008).…”