Transcriptomic and phenotypic analysis of the effects of T-2 toxin on Saccharomyces cerevisiae: evidence of mitochondrial involvement.

At 5 µg mL(-1) , T-2 toxin significantly upregulated the transcription of 281 genes and downregulated 86. Strongly upregulated genes included those involved in redox activity, mitochondrial functions, the response to oxidative stress, and cytoplasmic rRNA transcription and processing. Highly repressed genes have roles in mitochondrial biogenesis, and the expression and stability of cytoplasmic rRNAs. T-2 toxin inhibition of growth was greater in a medium requiring respiration, and was antagonized by antioxidants. T-2 toxin treatment induced reactive oxygen species, caused nucleolytic damage to DNA, probably mitochondrial, and externalization of phosphatidylserine. Deletion mutations causing respiratory deficiency substantially increased toxin tolerance, and deletion of some TOR (target of rapamycin) pathway genes altered T-2 toxin sensitivity. Deletion of FMS1, which plays an indirect role in cytoplasmic protein synthesis, markedly increased toxin tolerance. Overall, the findings suggest that T-2 toxin targets mitochondria, generating oxy-radicals and repressing mitochondrial biogenesis genes, thus inducing oxidative stress and redox enzyme genes, and triggering changes associated with apoptosis. The large transcriptional changes in genes needed for rRNA transcription and expression and the effects of deletion of FMS1 are also consistent with T-2 toxin damage to the cytoplasmic translational mechanism, although it is unclear how this relates to the mitochondrial effects.

Cloning and expression of Penicillium minioluteum dextranase in Saccharomyces cerevisiae and its exploitation as a reporter in the detection of mycotoxins.

A dextranase gene from Penicillium minioluteum (strain IMI068219) has been cloned, sequenced and expressed in Saccharomyces cerevisiae via fusion of the DNA segment encoding the mature dextranase protein with alpha-factor signal sequence, and insertion into the GAL1-controlled expression vector pYES2/CT. Galactose-induced expression yielded extracellular dextranase activity of 0.63 units/ml and cell-associated dextranase activity of 0.48 units/ml, after 24 h incubation. The dextranase construct was introduced into a strain of S. cerevisiae expressing the human cytochrome P450 3A4 (CYP3A4) and the cognate reductase, which was then used to develop a microplate toxicity bioassay. Toxicity was signalled as inhibition of dextranase activity, assayed fluorimetrically. This novel bioassay was assessed using six economically significant mycotoxins.

The occurrence of mycotoxins in key commodities in Bangladesh: surveillance results from 1993 to 1995.

A three-year surveillance program assessed the extent of mycotoxin contamination of key foods and feeds grown in Bangladesh. The study also included groundnuts utilized as snack food. In the first two phases of the program the samples collected were analyzed only for aflatoxins, but in the third phase, as well as for aflatoxins, samples were tested for the presence of fumonisin B1, ochratoxin A, zearalenone, deoxynivalenol, and T-2 toxin. Of the foods and feeds tested, the incidence of aflatoxin contamination varied from low (rice collected from farmers' stores, 8%) to high (maize, 67%). However, both the average total aflatoxin contents (< 1.0 microg/kg) and the maximum aflatoxin B1 contents (< or = 5.0 microg/kg) recorded for pulses, rice and its various products, and wheat were low. On the other hand, the levels of contamination of maize, roasted and raw groundnuts, and poultry feed were considerably higher, with average total aflatoxin B1 contents of 33, 13, 65, and 7 microg/kg, respectively, and maximum aflatoxin B1 contents of 245, 79, 480, and 160 microg/kg, respectively. Fumonisin B1, ochratoxin A, zearalenone, deoxynivalenol, and T-2 toxin were found, to any significant extent, only in some of the maize samples tested, always accompanied by aflatoxins. One sample of maize contained five mycotoxins, namely, the aflatoxins, fumonisin B1, deoxynivalenol, zearalenone, and ochratoxin A. In a limited trial using hospital staff in Dhaka, the analysis of the aflatoxin-albumin adduct in serum showed that approximately half of the test group had been recently exposed to low levels of aflatoxins.