Process development for the elucidation of mycotoxin formation in Alternaria alternata.

Katrin Brzonkalik,Anke Neumann,Christoph Syldatk,Tanja Herrling

doi:10.1186/2191-0855-1-27

Abstract

The black mould Alternaria alternata produces a wide diversity of mycotoxins which are of particular health concern. Since no maximum allowable limits are set for Alternaria toxins in food and feed, prevention of Alternaria infestations and mycotoxin spoilage is the only way to avoid health risks. Thus, the understanding of mycotoxin biosynthesis is essential. For that purpose, a reliable batch process in a 2 L bioreactor was established which enables the study of several parameters influencing the production of the mycotoxins alternariol (AOH), alternariol monomethylether (AME) and tenuazonic acid (TA) by A. alternata DSM 12633. Modified Czapek-Dox medium was used with glucose as carbon source and ammonium and nitrate as nitrogen sources. Consumption of carbon and nitrogen sources as well as formation of the three mycotoxins were monitored; the average data of five independent fermentations was plotted and fitted using a logistic equation with four parameters. Maximum mycotoxin concentrations of 3.49 ± 0.12 mg/L AOH, 1.62 ± 0.14 mg/L AME and 38.28 ± 0.1 mg/L TA were obtained.In this system the effect of different aeration rates (0.53 vvm-0.013 vvm) was tested which exerted a great influence on mycotoxin production. The use of the semi-synthetic Czapek-Dox medium allowed the exchange of carbon and nitrogen sources for acetate and aspartic acid. The use of acetate instead of glucose resulted in the sole production of alternariol whereas the exchange of ammonium and nitrate for aspartate enhanced the production of both AOH and AME while TA production was not affected.

Highlights

Mycotoxins are secondary metabolites of low molecular weight produced by filamentous fungi
In a first experiment glucose was exchanged for 22.66 g/L sodium acetate trihydrate and in a second experiment the mixture of ammonium chloride and sodium nitrate was exchanged for 0.54 g/L aspartic acid
Process parameters of A. alternata fermentation in a 2 L bioreactor system To elucidate the reproducibility of the system five independent fermentations were performed

Summary

Introduction

Mycotoxins are secondary metabolites of low molecular weight produced by filamentous fungi. Since the discovery of the first mycotoxins, the aflatoxins, in 1960 which caused the death of 10,000 turkeys many new mycotoxins have been identified in the last 50 years. Today 300 to 400 compounds are designated as mycotoxins (Bennett and Klich 2003,). As other secondary metabolites mycotoxins are formed subsequently to the growth phase and are not necessary for growth or development (Fox and Howlett 2008,). Mycotoxin formation is subjected to a complex regulation, but it is often induced by nutrient limitation (Demain 1986,). Mycotoxins are released by the fungus in the surrounding substrate and contamination of agricultural products is

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