Influence of ochratoxin A on adaptation of Penicillium nordicum on a NaCl-rich dry-cured ham-based medium

Iberian dry-cured ham is an important meat product with high consumption worldwide. The special ecological conditions occurring throughout its ripening favour surface colonisation of filamentous fungi. Normally, moulds contribute to the development of the sensory qualities of the ham; however, some toxigenic species, such as Penicilllum nordlcum, are able to successfully adapt to the NaCI-rich environment found in dry -cured ham and produce ochratoxin A (OTA) in this product. Moreover, it was suggested that the biosynthesis of OTA by P. nordicwn itself may support the adaptation to this food environment. However, this mechanism has not been completely elucidated yet. The objective of this work was to evaluate the influence of different concentrations of commercial OTA (cOTA, at 0, 0.2, 1 and 5 ppb) on growth rate, biosynthetic- and stress-related gene expression and OTA production by two P. nordicum strains (Pn15 and Pn69) on dry -cured ham based-media. Two NaCI conditions (0% and 10%) were evaluated for each cOTA level. In general, no intra-strain and inter-strain differences in growth rates were found among the conditions tested. The stress-related Hogl gene expression of the strain Pn15 was affected by cOTA and NaCI concentration whilst the strain Pn69 was not affected by these variables. The expression of OTA-related otopks and otwips genes of the strain Pn15 was affected by several NaCl and cOTA combinations. However, the strain Pn69 showed no differences in relative gene expression. Regarding to OTA production, different behaviours were displayed by the two strains. The strain Pn15, which produced high OTA amounts by itself, produced OTA without the necessity of the presence of NaCl or cOTA as stressors. However, the presence of cOTA triggers OTA production by the weak OTA producing Pn69 in the absence of NaCI. In addition, although a moderate correlation was found between the expression of the OTA-related genes and mycotoxin produced by P. nordicwn in the absence of NaCl, none was obtained between Hogl gene expression and mycotoxin production. This study is a step forward for a better understanding of the ability of P. nordicum producers of OTA to colonise NaCl-rich habitats such as Iberian ham for proposing actions to minimise OTA contamination in this meat product.