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Toxins 2019, 11(2), 107; https://doi.org/10.3390/toxins11020107

Inhibition of Aflatoxin Production by Paraquat and External Superoxide Dismutase in Aspergillus flavus

Department of Biosciences, Teikyo University, 1-1 Toyosatodai, Utsunomiya 320-8551, Japan
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Received: 15 January 2019 / Revised: 11 February 2019 / Accepted: 12 February 2019 / Published: 12 February 2019
(This article belongs to the Collection Aflatoxins)
PDF [976 KB, uploaded 12 February 2019]

Abstract

Aflatoxin contamination of crops is a worldwide problem, and elucidation of the regulatory mechanism of aflatoxin production, for example relative to the oxidative–antioxidative system, is needed. Studies have shown that oxidative stress induced by reactive oxygen species promotes aflatoxin production. However, superoxide has been suggested to have the opposite effect. Here, we investigated the effects of the superoxide generator, paraquat, and externally added superoxide dismutase (SOD) on aflatoxin production in Aspergillus flavus. Paraquat with an IC50 value of 54.9 µM inhibited aflatoxin production without affecting fungal growth. It increased cytosolic and mitochondrial superoxide levels and downregulated the transcription of aflatoxin biosynthetic cluster genes, including aflR, a key regulatory protein. The addition of bovine Cu/ZnSOD to the culture medium suppressed the paraquat-induced increase in superoxide levels, but it did not fully restore paraquat-inhibited aflatoxin production because bovine Cu/ZnSOD with an IC50 value of 17.9 µg/mL itself inhibited aflatoxin production. Externally added bovine Cu/ZnSOD increased the SOD activity in fungal cell extracts and upregulated the transcription of genes encoding Cu/ZnSOD and alcohol dehydrogenase. These results suggest that intracellular accumulation of superoxide impairs aflatoxin production by downregulating aflR expression, and that externally added Cu/ZnSOD also suppresses aflatoxin production by a mechanism other than canonical superoxide elimination activity.
Keywords: aflatoxin production; Aspergillus flavus; superoxide; paraquat; superoxide dismutase aflatoxin production; Aspergillus flavus; superoxide; paraquat; superoxide dismutase
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Furukawa, T.; Sakuda, S. Inhibition of Aflatoxin Production by Paraquat and External Superoxide Dismutase in Aspergillus flavus. Toxins 2019, 11, 107.

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