|Crespo-sempere, Ana - University Of Valencia|
|Selma-lazaro, Cristina - University Of Valencia|
|Palumbo, Jeffrey - Jeff|
|Gonzalez-candelas, Luis - University Of Valencia|
|Martinez-culebras, Pedro - University Of Valencia|
Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2015
Publication Date: 1/22/2015
Publication URL: http://handle.nal.usda.gov/10113/61672
Citation: Crespo-Sempere, A., Selma-Lazaro, C., Palumbo, J.D., Gonzalez-Candelas, L., Martinez-Culebras, P.V. 2015. Effect of oxidant stressors and phenolic antioxidants on the ochratoxigenic fungus aspergillus carbonarius. Journal of the Science of Food and Agriculture. doi: 10.1002/JSFA.7077.
Interpretive Summary: Aspergillus carbonarius is a fungus that produces the toxic chemical ochratoxin A (OTA). This fungus commonly grows on grapes, where it is exposed to environmental stresses, including oxidative stress. We tested whether exposure to chemicals that cause oxidative stress (such as hydrogen peroxide and menadione) or chemicals that act as antioxidants to relieve oxidative stress (such as catechin and grape-produced chemicals including resveratrol) affect the growth of A. carbonarius, OTA production, and expression of genes involved in fungal oxidative stress response. After exposure to oxidative stress-causing chemicals, the fungus produced OTA, showing that OTA production is one component of the fungal response to oxidative stress. Also, exposure to high levels of antioxidant chemicals caused a stress response that appeared similar to an oxidative stress response, resulting in higher production of OTA and slower fungal growth. The expression of two genes that protect the fungus from oxidative stress is generally lower when the fungus is producing OTA, suggesting that OTA production is another way the fungus can be protected from oxidative stress. On the other hand, the grape compound resveratrol caused higher expression of oxidative stress-response genes as well as higher OTA production, suggesting that the fungus responds to resveratrol using both protective mechanisms. These results increase our understanding of what environmental conditions contribute to the production of OTA, and why the fungus is making OTA. This may lead to the development of chemical tools that can be used to reduce the potential for OTA contamination of grapes.
Technical Abstract: In this work, the effect of oxidant stressors (hydrogen peroxide, menadione) and antioxidants (BHT, phenolic antioxidants) on growth, ROS generation, OTA production and gene expression of antioxidant enzymes of A. carbonarius was studied. In comparison to a nontoxigenic strain, an OTA-producing A. carbonarius strain was more sensitive to the oxidative stress caused by H2O2, suggesting a decreased ability of the toxigenic strain to adapt efficiently to the oxidative stress. Additionally, when a culture of A. carbonarius was amended with 5 mM of H2O2, OTA production was stimulated. The exposure to increasing concentrations of menadione led to higher levels of ROS, which were correlated with increased amounts of OTA, highlighting a close relationship between oxidative stress and OTA production in A. carbonarius. Concentrations of the synthetic antioxidant BHT higher than 2.5 mM, inhibited growth and increased ROS generation and OTA production. After exposure to naturally occurring concentrations of catechin and polyphenolic extract, no significant inhibition in growth was observed. Nevertheless, they produced widely different effects on OTA production depending on the antioxidant concentration used. In the case of resveratrol, there was a slight, but statistically significant inhibition in growth at the highest concentration tested (1500 µM). In general, gene expression of antioxidant enzymes (SOD and PRX) was down regulated after exposure to oxidant and antioxidant concentrations that enhanced OTA production. However, sod and prx genes were up regulated at concentrations of resveratrol that increases OTA production, suggesting that these antioxidant enzymes might participate in the fungal response to oxidative stress induced by resveratrol.