Sclerotia Formation and Toxin Production in Large Sclerotial &amp;lt;i&amp;gt;Aspergillus flavus&amp;lt;/i&amp;gt; Isolates from Kenya

S A Okoth,V Joutsjoki,V Ayugi,H Korhonen,B Nyongesa,E K Kang’Ethe

doi:10.4236/aim.2016.61005

Abstract

We studied the relationship between sclerotia formation and aflatoxin production by Aspergillusflavus strains isolated from maize kernels from Nandi County. Isolates recovered from maize kernels were tested for their ability to form sclerotia on different growth media. PCR analysis was done on the isolates to detect 2 structural genes, aflD and aflQ, involved in aflatoxin biosynthesis pathway. Positive A. flavus isolates for one or both genes were grown on Yeast Extract Sucrose Agar medium and aflatoxins quantified using LCMSMS. All the isolates formed large sclerotia and their formation was influenced by media type but could not be related to amount of aflatoxins produced both in vivo and in vitro. Though sclerotia are perennating structures and so contribute to survival index of a fungus, their initiation is regulated by external factors though ability to form is genetic. This brings ambiguity of their presence or abundance as a measure of toxicity.

Highlights

Aspergillus Section Flavi is the major group of fungi associated with aflatoxin contamination in several agricultural commodities
This study explored the possibility of using the ability to form sclerotia as indication of toxigenicity among the large sclerotia formers isolated from maize in Nandi County, Kenya
The aflD gene encodes an enzyme that catalyzes the conversion of the first stable aflatoxin biosynthesis intermediate, norsolorinic acid to averantin [5] while the aflQ gene is involved in the conversion of O-methylsterigmatocystin to aflatoxin B1 (AFB1) and aflatoxin G1 (AFG1) and dihydro-O-methylsterigmatocystin to aflatoxin B2 (AFB2) and aflatoxin G2 (AFG2) [6]

Summary

Introduction

Aspergillus Section Flavi is the major group of fungi associated with aflatoxin contamination in several agricultural commodities. (2016) Sclerotia Formation and Toxin Production in Large Sclerotial Aspergillus flavus Isolates from Kenya. Ability to form sclerotia and formation of metabolites has been associated with virulence in fungi [2]. Erlich and Mark [4] reported that the timing of expression for some of the gene clusters for secondary metabolism in Aspergillus flavus was coordinated with sclerotial production and that the associated metabolites accumulated preferentially in sclerotia. This study explored the possibility of using the ability to form sclerotia as indication of toxigenicity among the large sclerotia formers isolated from maize in Nandi County, Kenya. Aspergillus flavus isolates were analyzed for the presence of two aflatoxin biosynthesis genes in relation to their capability to produce aflatoxins, targeting the structural genes aflD, and aflQ genes. The aflD gene encodes an enzyme that catalyzes the conversion of the first stable aflatoxin biosynthesis intermediate, norsolorinic acid to averantin [5] while the aflQ gene is involved in the conversion of O-methylsterigmatocystin (omst) to aflatoxin B1 (AFB1) and aflatoxin G1 (AFG1) and dihydro-O-methylsterigmatocystin (dmdhst) to aflatoxin B2 (AFB2) and aflatoxin G2 (AFG2) [6]

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Discussion

Conclusion