Monitoring the Temporal Expression of Genes Involved in Ochratoxin A Production of Aspergillus carbonarius under the Influence of Temperature and Water Activity.

Iliada Lappa,Dimosthenis Kizis,Efstathios Panagou

doi:10.3390/toxins9100296

Iliada Lappa, Dimosthenis Kizis + Show 1 more

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https://doi.org/10.3390/toxins9100296

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Abstract

The objective of this study was to investigate the effect of environmental factors, namely temperature and water activity, on genes involved in the regulation of ochratoxin A (OTA) production over time. For this purpose, the previously characterized toxigenic Aspergillus carbonarius Ac29 isolate from Greek vineyards and the A. carbonarius ITEM 5010 reference strain were subjected to combined temperature and water activity (aw) treatments to study OTA production and relative gene expression. The fungal isolates were grown on a synthetic grape juice liquid medium (SGM) under different temperature (20 °C, 25 °C and 30 °C) and aw (0.94 and 0.98) regimes. The expression of the AcOTApks, AcOTAnrps, and laeA OTA related genes was investigated using real time PCR. Gene expression was monitored at the same time points, along with fungal biomass and OTA accumulation at three, six and nine days of incubation. In gene expression analysis, stimulation of the biosynthetic genes was observed a few days before any toxin could be detected. This fact may underline a possible early indicator of potential toxin contamination of grapes. However, the transcript levels varied with respect to the different combinations of ecophysiological conditions and time, highlighting a complex regulation of OTA related gene expression of A. carbonarius in the specific medium.

Highlights

Ochratoxin A (OTA) is the most important mycotoxin encountered in grapes and grape products, which is widely distributed as a natural contaminant
Two-dimensional (2D) contour plots representing biomass production (g) of A. carbonarius Ac29 and A. carbonarius ITEM 5010 in relation to temperature and incubation time for each aw level assayed are shown in Figure 1
These results indicate that the combination of specific temperature and water activity has an important effect on fungal growth

Summary

Introduction

Ochratoxin A (OTA) is the most important mycotoxin encountered in grapes and grape products, which is widely distributed as a natural contaminant. It is categorized as group 2B carcinogen by the World Health Organization (WHO) [1] as it displays nephrotoxic, hepatotoxic, teratogenic and immunosuppressive properties affecting seriously human health. Ochratoxins (OTs) are secondary metabolites produced by several species of filamentous fungi belonging to the Aspergillus or Penicillium genera. Aspergillus carbonarius is considered the most important OTA producer in grapes, especially for those cultivated in warm climates [2]. The basic chemical structure of OTs, concerning OTA, OTB, and OTC, consists of an isocumarin nucleus bonded to a L-phenylalanine unit by an amide bond. OTA is the chlorinated form of the toxin, which is most prevalent, whereas B and C, the non-chlorinated and esterified forms, respectively [3]

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