Metabolism of glutamic acid in Aspergillus ochraceus during the biosynthesis of ochratoxin A

RNA-Seq Reveals OTA-Related Gene Transcriptional Changes in Aspergillus carbonarius

Ochratoxin A (OTA) is a mycotoxin harmful for animals and humans. Aspergillus carbonarius is the main responsible for OTA contamination of grapes and derived products. Gene transcriptional profiling of 4 A. carbonarius strains was carried out by RNA-Seq analysis to study transcriptome changes associated with OTA production. By comparing OTA inducing (OTAI) vs. non-inducing (OTAN) cultural conditions, a total of 3,705 differentially expressed genes (DEGs) (fold change > |2| and FDR ≤ 0.05) were identified. Several genes involved in primary metabolic processes, with particular regard to carbohydrate and amino acid metabolisms, secondary metabolic processes, transport, response to stress and sporulation were up-regulated by OTAI conditions at all the analysed sampling times (4, 6 and 8 DAI) or starting from 6 DAI. Highly up-regulated DEGs encoding enzymes involved in biosynthesis of secondary metabolites, oxidoreductases, transporters and transcription factors were examined for their potential involvement in OTA biosynthesis and related metabolic pathways. Differential expression of genes encoding polyketide synthases (pks), non-ribosomal peptide synthetases (nrps) and chloroperoxidase (cpo) was validated by RT-qPCR. Among clusters of co-regulated genes involved in SM biosynthesis, one putative OTA-gene cluster, including both pks and nrps genes, was detected in the A. carbonarius genome.

Production of(14)C-ochratoxin A byPenicillium verrucosum sp. 1761 in liquid culture

The synthesis of(14)C-labelled ochratoxin A was carried out by biosynthesis withPénicillium verrucosum sp. 1761 in liquid culture using 2-(14)C-Na-acetate and 2-(14)C-malonic acid as precursor. The largest amount of ochratoxin A produced byPénicillium verrucosum was detected in a minimal medium after an incubation period of 28 days. By addition of citric acid and 2,4-dichlorophenoxy acetic acid larger ochratoxin A contents could be measured. For transformation studies of ochratoxin A, a molecule which is exclusively labelled in the isocoumarin moiety is best suitable. This labelling could be obtained by using labelled malonic acid as precursor, whereas with 2-(14)C-Na-acetate as precursor the whole molecule was labelled. Incorporation rates of radioactivity into the molecule were from 0.04% to 0.11%, specific radioactivities from 0.02 μCi/mg to 0.07 μCi/mg.

Postharvest production of ochratoxin A by Aspergillus ochraceus and Penicillium viridicatum in barley with different protein levels

The production of ochratoxin A (OA) in barley by Aspergillus ochraceus and Penicillium viridicatum was measured at 12 and 25 degrees C. The grain had been fertilized with various amounts of nitrogen fertilizer (0, 90, or 240 kg/ha) and contained (at crop maturity) 9.1, 10.4, or 12.0% protein, respectively. The production of OA by both fungi increased as the protein concentration increased. Glutamic acid and proline were enriched relative to other amino acids as the protein concentration increased. The differences in OA production could not be explained by a differential effect of protein or amino acids on fungal growth in barley. However, glutamic acid and proline enhanced OA production in liquid cultures of both A. ochraceus and P. viridicatum.

Screening of zearalenone-producing Fusarium species in Egypt and chemically defined medium for production of the toxin

296 isolates of Fusarium spp. from 100 samples of ccereal grains were examined for their ability to produce zearalenone on liquid culture medium. Thin layer chromatographic analysis revealed that the mycotoxin was detected from 45 isolates, (F. oxysporum), 36; F. moniliforme, 8; and F. equiseti, one isolate). A suitable liquid medium and some optimal conditions for the biosynthesis of zearalenone were reported. Glutamine and riboflavin stimulated the production of the toxin. The maximum amount of zearalenone appeared at pH 7, after 12 days of incubation at 20 degrees C.

Media for identification of Gibberella zeae and production of F-2-(Zearalenone)

Media are described for the isolaton of Fusarium graminearum in the perithecial state, Gibberella zeae, and for the production of F-2 (zearalenone) by Fusarium species. On soil extract-corn meal agar isolated medium, G. Zeae produced perithecia in 9 to 14 days under a 12-h photoperiod. Species of Fusarium were screened for F-2 production on a liquid medium. From strains that produced F-2, the yields, from stationary cultures of G. zeae and F. culmorum after 12 days of incubation, ranged from 22 to 86 mg/liter. Three strains produced no F-2. Glumatic acid, starch, yeast extract,and the proper ratio of medium volume-to-flask volume were necessary for F-2 synthesis.