In order to better understand the variation in aflatoxin-producing potential among wild type isolates of Aspergillus parasiticus, we have devised a method for inducing non-toxigenic variants from wild type and mutant strains of this species. After 5-10 transfers of mycelial macerates in a defined medium, we have routinely isolated variant forms with lowered sporu-lation, reduced mycelial pigmentation, and absence of sclerotium formation. We have named these strains “sec-” for “secondary metabolism negative”.
The effect of T-2, HT-2 and diacetoxyscirpenol (DAS) on growth and fermentation in Kluyveromyces marxianus was examined. Both T-2 and DAS were inhibitory to aerobic growth of this yeast; there was an inverse linear relationship between toxin concentration and the dry mass of cultures, with sensitivity to T-2 being approx. 13 times that to DAS. At a concentration of 5μg T-2/ml culture medium caused reduction in viability of cells relative to controls in both K. marxianus and Saccharomyces cerevisiae within 3h, but by 6h there was marked recovery of viability in S. cerevisiae. With 5μg HT-2/ml, there was only slight retardation of growth at 3h, and recovery or stimulation of growth by 6h. A trend to increasing cell-size with exposure to increasing T-2 concentration was evident by 4h, and by 24h was pronounced in both mother cells and single cells in actively budding cultures. In fermentations of glucose-amended malt extract broth containing up to 5μg T-2/ml there was a concentration-dependent lag before attenuation of fermentable sugars and production of ethanol was measurable, but thereafter the rate of fermentation was similar to controls. As in earlier work with S. cerevisiae, DAS had less effect than T-2 on fermentation.
The purpose of the work was to investigate the ability of the Penicillium fungi to synthesize nitrogen-containing mycotoxins. Most fungi of the genus were shown to produce various classes of mycotoxins such as ergot alkaloids, diketopiperazines, quinoline alkaloids. The dependence of the activity of the producer on cultivation conditions and their physiological states were investigated. Methods of isolation, purification and analysis of both previously known and new mycotoxins were developed.
Each 10kg of high moisture maize kernels (moisture content (mc) 29.1%) inoculated with Aspergillus flavus was packed in various kinds of package. Every bag was sealed with string so as to make the air space to be as little as possible. In traditional jute bag and fabricated polypropylene (PP) bag, A. flavus infection occurred completely within 4 to 6 days. Thick polyethylene (PE) bag (125μm thick) and high density PE bag (40μm thick) perfectly in hibited the growth of A, fiavus for over 20 days and no aflatoxin was detected. Wet maize kernels with various maturity levels and mc (97 to 125 days after planting and mc 21.3% to 33.4%) were also prevented from A. flavus infection completely in the thick PE bag.
Recently we have demonstrated that the growth of Kagura-2 cells established from aflatoxin B1 (AFB1)-induced rat hepatoma was markedly stimulated by glucocorticoids (GCs). To investigate a possible role of GCs in the growth of Kagura-2 cells, we studied the effect of conditioned medium (CM) prepared from Kagura-2 cells on the neuronal differentiation of pheochromocytoma (PC12) cells. Kagura-2 cell-CM caused in PC12 cells a number of physiological changes which mimic the nonreplicating sympathetic neuron-like cells, including induction of neurite extension and acetylcholinesterase activity. The neuronal differentiation factor(s) in CM were inactivated by the treatments of trypsin, acetic acid, dithiothreitol and heat. The molecular weights of factor(s) ranged from 6, 000 to 14, 000 on the basis of experiments using various molecular weight cutoff dialysis tubing and gel filtration.
A rapid and 1-step clean-up method for determination of ochratoxin A (OTA) was developed by anti OTA monoclonal antibody affinity chromatography. This method offered good recovery and significantly cleaner HPLC chromatograms than conventional approaches. This affinity column was regenerated for many times with no apparent loss of activity. The detection limit of OTA was 0.5 ppb.