Physiological relationship between food preservatives, environmental factors, ochratoxin and otapksPV gene expression by Penicillium verrucosum.

There is significant interest in trying to understand the relationship between environmental factors, preservative concentration and expression of genes involved in mycotoxin production. However, little information is available on the link between physiological stress factors and expression of genes responsible for mycotoxin production. This study has examined the effect of interactions between ionic and non-ionic water availability modified with glycerol or NaCl (a(w), 0.98, 0.95 and 0.93) and sub-optimal concentrations of calcium propionate and potassium sorbate (150, 300 ppm) at 25 degrees C on growth, ochratoxin A (OTA) and otapksPV gene expression by the mycotoxigenic species Penicillium verrucosum. Growth was inhibited between 25-35% by the preservatives at each a(w) level. However, OTA production was stimulated by 150 and 300 ppm of both preservatives, especially at 0.95 and 0.93 a(w). If water activity as a single stress factor was changed, a typical OTA production and otapksPV expression profile occurred, indicating that OTA biosynthesis is activated under two conditions, i.e., under optimal growth conditions and under weak stress conditions. Temporal analysis of otapksPV expression showed that there was an optimum after 8-9 days incubation. Statistical analyses indicated good correlation between sub-optimal concentrations of preservatives, intermediate a(w) levels and genotypic and phenotypic gene and toxin production. This is the first time that genotypic information has been linked to phenotypic mycotoxin production in relation to such interacting stress factors.