Interacting climate change environmental factors effects on Fusarium langsethiae growth, expression of Tri genes and T-2/HT-2 mycotoxin production on oat-based media and in stored oats

The objectives of this study were to investigate the impact that interactions between key climate change (CC) related environmental factors of temperature (20, 25, 30°C), water activity (aw; 0.995, 0.98) and CO2 exposure (400, 1000 ppm) may have on (a) growth, (b) gene expression of biosynthetic toxin genes (Tri5, Tri6, Tri16), and (c) phenotypic T-2/HT-2 production by Fusarium langsethiae on oat-based agar medium and in stored oats. Fungal growth was optimum at 25°C and 0.995 aw and reduced significantly at 30°C and intermediate stress (0.98 aw, elevated CO2 (1000 ppm) exposure by approx. 4-fold. Lag phases prior to growth paralleled these results with the longest lag phase in this treatment (24 hrs). On oat-based medium, the relative Tri5 gene expression was increased in elevated CO2 conditions. The expression of both the Tri6 and Tri16 genes was reduced when compared to control (20°C, 0.995 aw, 400 ppm), especially in elevated CO2 conditions. In stored oats, the Tri5 gene expression was reduced in all conditions except at 30°C, 0.98 aw, elevated CO2 where there was a significant (5.3-fold) increase. The expression of the Tri6 was slightly over-expressed in elevated CO2 and the Tri16 gene was upregulated, especially in elevated CO2 conditions. For mycotoxin production, both on oat-based medium and in stored oats the production was higher at 25°C when compared to 30°C. In stored oats, at 0.98 aw, elevated CO2 led to higher T2/HT-2 toxin production at both 25 and 30°C with a significant increase (73-fold higher) at 30°C. In elevated CO2 conditions, Tri16 (Spearman test; 0.68; p-value=0.0019) and Tri5 gene expression (Spearman test; 0.56; p-value=0.0151) were correlated with T-2+HT-2 production. Nine T-2 and HT-2 metabolites were detected by LC-MS/MS including a new dehydro T-2 toxin and the conjugate, HT-2 toxin glucuronide (in plantae). The new dehydro T-2 toxin was the most abundant metabolites and showed correlation (R2=0.8176) with T-2 production.

This is the first study to examine the impact of CC factors on growth and mycotoxin production by a strain of F. langsethiae. The influence of such scenarios on relative risk of oats contamination with these toxins in relation to the food security agenda is discussed.