Effects of temperature and water activity change on ecophysiology of ochratoxigenic Aspergillus carbonarius in field-simulating conditions.

Ochratoxin A (OTA) is the primary mycotoxin threat in wine and dried vine fruits. Its presence in grape and wine is strongly related to climatic conditions and the expected climate change could represent a risk of increasing fungal colonization and OTA contamination in grapes. In this regard, the interacting effect of i) different conditions of water availability (0.93 and 0.99aw) and ii) different 10 h/14 h dark/light alternating temperature conditions simulating a nowadays (18/31 °C) and climate change scenario (20/37 °C) in high OTA risk areas of Apulia region, were studied. Lag phases prior to growth, mycelial growth rate, the expression of biosynthesis, transcription factors and regulatory genes of OTA cluster and OTA production were analysed in Aspergillus carbonarius ITEM 5010 under the combined effect of different climatic factors. At 18/31 °C and under water stress conditions (0.93 aw) the growth rate was slower than at 0.99 aw; on the contrary, at 20/37 °C a higher growth rate was observed at 0.93 aw. An over-expression of OTA genes and genes belonging to the global regulator Velvet complex was observed at 18/31 °C and 0.99 aw, with the specific OTA pathway transcription factor bZIP showing the highest expression level. The up-regulated transcription profile of the genes positively correlated with OTA production higher at 18/31 °C than at 20/37 °C and 0.99 aw; while no OTA production was detected at 0.93 aw at each of the temperature conditions tested. These findings provide preliminary evidence that the possible increase of the temperature, likely to happen in some areas of the Apulia region, may results in a reduction of both A. carbonarius spoilage and OTA production in grapes.