Novel Prenylated Indole Alkaloids with Neuroprotection on SH-SY5Y Cells against Oxidative Stress Targeting Keap1–Nrf2

Oxidative stress has been implicated in the etiology of Parkinson’s disease (PD). Molecules non-covalently binding to the Keap1–Nrf2 complex could be a promising therapeutic approach for PD. Herein, two novel prenylated indole alkaloids asperpenazine (1), and asperpendoline (2) with a scarce skeleton of pyrimido[1,6-a]indole were discovered from the co-cultivated fungi of Aspergillus ochraceus MCCC 3A00521 and Penicillium sp. HUBU 0120. Compound 2 exhibited potential neuroprotective activity on SH-SY5Y cells against oxidative stress. Molecular mechanism research demonstrated that 2 inhibited Keap1 expression, resulting in the translocation of Nrf2 from the cytoplasm to the nucleus, activating the downstream genes expression of HO-1 and NQO1, leading to the reduction in reactive oxygen species (ROS) and the augment of glutathione. Molecular docking and dynamic simulation analyses manifested that 2 interacted with Keap1 (PDB ID: 1X2R) via forming typical hydrogen and hydrophobic bonds with residues and presented less fluctuation of RMSD and RMSF during a natural physiological condition.

iTRAQ proteome analysis of the antifungal mechanism of citral on mycelial growth and OTA production in Aspergillus ochraceus

BACKGROUND

Aspergillus ochraceus causes food spoilage and produces mycotoxin ochratoxin A (OTA) during storage of agricultural commodities. In this study, citral was used to inhibit A. ochraceus growth and OTA accumulation, proteomic analysis was employed to verify the mechanism of citral.

RESULTS

Citral was found to significantly inhibit fungal growth and mycotoxin production in A. ochraceus. Specifically, 75, 125, 150 and 200 μL L^-1 citral suppressed mycelial growth by 33%, 46%, 50% and 100%, respectively. Additionally, 75 μL L^-1 citral inhibited OTA accumulation by 25%. Proteomic analysis was performed to elucidate the inhibitory mechanism of citral on mycelial growth and OTA production at subinhibitory concentrations (75 μL L^-1 ). Proteomics analysis identified 2646 proteins in A. ochraceus fc-1, of which 218 were differentially expressed between control and 75 μL L^-1 citral treatment samples. Differentially expressed proteins were identified by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses of biological process, cellular component and molecular function terms. Potential factors affecting mycelial growth and OTA production were analysed, and OTA production was revealed to be a complex process involving many associated factors related to various processes including nutrient intake, sterol biosynthesis, ribosome biogenesis, energy metabolism, oxidative stress and amino acid metabolism. In addition, citral at 75 μL L^-1 down-regulated OTA biosynthetic genes including pks and nrps, but slightly up-regulated the global regulatory factors veA, velB and laeA.

CONCLUSION

The findings further demonstrate the potential of citral for the preservation of grains and other agricultural products, and provide new insight into its antifungal mechanisms at subinhibitory concentrations. © 2021 Society of Chemical Industry.

Mycoviruses mediate mycotoxin regulation in Aspergillus ochraceus

To date, no demonstration of a direct correlation between the presence of mycoviruses and the quantitative or qualitative modulation of mycotoxins has been shown. In our study, we transfected a virus-free ochratoxin A (OTA)-producing isolate of Aspergillus ochraceus with purified mycoviruses from a different A. ochraceus isolate and from Penicillium aurantiogriseum. Among the mycoviruses tested, only Aspergillus ochraceus virus (AoV), a partitivirus widespread in A. ochraceus, caused a specific interaction that led to an overproduction of OTA, which is regulated by the European Commission and is the second most important contaminant of food and feed commodities. Gene expression analysis failed to reveal a specific viral upregulation of the mRNA of genes considered to play a role in the OTA biosynthetic pathway. Furthermore, AoOTApks1, a polyketide synthase gene considered essential for OTA production, is surprisingly absent in the genome of our OTA-producing isolate. The possible biological and evolutionary implications of the mycoviral regulation of mycotoxin production are discussed.

Antifungal and anti-mycotoxin efficacy of biogenic silver nanoparticles produced by Fusarium chlamydosporum and Penicillium chrysogenum at non-cytotoxic doses

The cell-free culture filtrate (CFF) of the fungi Fusarium chlamydosporum NG30 and Penicillium chrysogenum NG85 was tested to synthesize silver nanoparticles (AgNPs). The synthesized AgNPs were further characterized by means of transmission electron microscopy (TEM), dynamic light scattering (DLS) and Fourier transform infra-red (FTIR) spectroscopy. TEM revealed their spherical shape, homogeneity and a size range between 6 and 26 nm for F. chlamydosporum AgNPs (FAgNPs) and from 9 to 17.5 nm for P. chrysogenum AgNPs (PAgNPs). DLS showed that the diameter of FAgNPs was narrower than that of PAgNPs. FTIR spectroscopy indicated that the functional groups present in the CFF might be responsible for the reduction of silver ions to form stabilized protein-capped AgNPs. In addition, the AgNPs showed notable antifungal activity and potency in thwarting mycotoxin production. Thus, using Aspergillus flavus as a test microorganism the minimum inhibitory concentration (MIC) was 48, 45 and 50 μg/mL for FAgNPs, PAgNPs and the antifungal compound itraconazole, respectively. Also, when testing Aspergillus ochraceus FAgNPs, PAgNPs and itraconazole led to MIC values of 51, 47 and 49 μg/mL, respectively. The statistical MIC values to inhibit completely the total aflatoxin production by A. flavus were 5.9 and 5.6 μg/mL for FAgNPs and PAgNPs, respectively, and to inhibit the ochratoxin A production by A. ochraceus 6.3 and 6.1 μg/mL for FAgNPs and PAgNPs, respectively. The cytotoxicity assay of the AgNPs on human normal melanocytes (HFB 4) revealed a cell survival of 80% and 75% at a concentration of 6 μg/mL for FAgNPs and PAgNPs, respectively.

Cryptic Secondary Metabolites from the Sponge-Associated Fungus Aspergillus ochraceus

The fungus Aspergillus ochraceus was isolated from the Mediterranean sponge Agelas oroides. The initial fermentation of the fungus on solid rice medium yielded 16 known compounds (4⁻19). The addition of several inorganic salts to the rice medium mainly influenced the accumulation of these secondary metabolites. Fermentation of the fungus on white bean medium yielded the new waspergillamide B (1) featuring an unusual p-nitrobenzoic acid as partial structure. Moreover, two new compounds, ochraspergillic acids A and B (2 and 3), which are both adducts of dihydropenicillic acid and o- or p-aminobenzoic acid, were isolated from the co-culture of the fungus with Bacillus subtilis. Compound 2 was also detected in axenic fungal cultures following the addition of either anthranilic acid or tryptophan to the rice medium. The structures of the new compounds were established by 1D and 2DNMR experiments as well as from the HRMS data. The absolute configuration of 1 was elucidated following hydrolysis and derivatization of the amino acids using Marfey's reagent. Viomellein (9) and ochratoxin B (18) exhibited strong cytotoxicity against the A2780 human ovarian carcinoma cells with IC50 values of 5.0 and 3.0 µM, respectively.

Influence of high-pressure processing on the generation of γ-aminobutyric acid and microbiological safety in coffee beans

BACKGROUND

The aim of this study was to investigate the influence of high-pressure processing (HPP) on γ-aminobutyric acid (GABA) content, glutamic acid (Glu) content, glutamate decarboxylase (GAD) activity, growth of Aspergillus fresenii, and accumulated ochratoxin A (OTA) content in coffee beans.

RESULTS

The results indicated that coffee beans subjected to HPP at pressures ≥50 MPa for 5 min increased GAD activity and promoted the conversion of Glu to GABA, and showed a significantly doubling of GABA content compared with unprocessed coffee beans. Additionally, investigation of the influence of HPP on A. fresenii growth on coffee beans showed that application ≥400 MPa reduced A. fresenii concentrations to <1 log. Furthermore, during a 50-day storage period, we observed that a processing pressure of 600 MPa completely inhibited A. fresenii growth, and on day 50 the OTA content of coffee beans subjected to processing pressures of 600 MPa was 0.0066 μg g^-1 , which was significantly lower than the OTA content of 0.1143 μg g^-1 in the control group.

CONCLUSION

This study shows that HPP treatment can simultaneously increase GABA content and inhibit the growth of A. fresenii, thereby effectively reducing the production and accumulation of OTA and maintaining the microbiological safety of coffee beans. © 2018 Society of Chemical Industry.

A Consensus Ochratoxin A Biosynthetic Pathway: Insights from the Genome Sequence of Aspergillus ochraceus and a Comparative Genomic Analysis

Ochratoxin A (OTA) is a toxic secondary metabolite produced by Aspergillus and Penicillium species that widely contaminates food and feed. We sequenced and assembled the complete ∼37-Mb genome of Aspergillusochraceus fc-1, a well-known producer of OTA. Key genes of the OTA biosynthetic pathway were identified by comparative genomic analyses with five other sequenced OTA-producing fungi: A. carbonarius, A. niger, A. steynii, A. westerdijkiae, and Penicillium nordicum OTA production was completely inhibited in the deletion mutants (ΔotaA, ΔotaB, ΔotaC, ΔotaD, and ΔotaR1), and OTA biosynthesis was restored by feeding a postblock substrate to the corresponding mutant. The OTA biosynthetic pathway was unblocked in the ΔotaD mutant by the addition of heterologously expressed halogenase. OTA biosynthesis begins with a polyketide synthase (PKS), OtaA, utilizing acetyl coenzyme A (acetyl-CoA) and malonyl-CoA to synthesize 7-methylmellein, which is oxidized to OTβ by cytochrome P450 monooxygenase (OtaC). OTβ and l-β-phenylalanine are combined by a nonribosomal peptide synthetase (NRPS), OtaB, to form an amide bond to synthesize OTB. Finally, OTB is chlorinated by a halogenase (OtaD) to OTA. The otaABCD genes were expressed at low levels in the ΔotaR1 mutant. A second regulator, otaR2, which is adjacent to the biosynthetic gene, could modulate only the expression of otaA, otaB, and otaD Thus, we have identified a consensus OTA biosynthetic pathway that can be used to prevent and control OTA synthesis and will help us understand the variation and production of the intermediate components in the biosynthetic pathway.IMPORTANCE Ochratoxin A (OTA) is a significant mycotoxin that contaminates cereal products, coffee, grapes, wine, cheese, and meat. OTA is nephrotoxic, carcinogenic, teratogenic, and immunotoxic. OTA contamination is a serious threat to food safety, endangers human health, and can cause huge economic losses. At present, >20 species of the genera Aspergillus and Penicillium are known to produce OTA. Here we demonstrate that a consensus OTA biosynthetic pathway exists in all OTA-producing fungi and is encoded by a gene cluster containing four highly conserved biosynthetic genes and a bZIP transcription factor.

UPLC-MS-IT-TOF Identification of Circumdatins Produced by Aspergillus ochraceus

A method based on the combined use of ultraperformance liquid chromatography coupled to mass spectrometry-ion trap-time-of-flight (UPLC-MS-IT-TOF) detection was employed to identify the metabolite production of Aspergillus ochraceus, which is the major cause of food and feed contamination due to ochratoxin A. Under the proposed chromatographic conditions, seven metabolites belonging to the family of circumdatins were separated and identified. Their initial identification was performed through the exact molecular formula, as a function of their accurate mass. Collision-induced dissociation was applied to predict precursor and product ions, and the elemental composition of each compound was obtained. The elimination of nitrogenous groups followed by successive losses of carbonyl groups is the common fragmentation pathway of circumdatins. With the fragmentation data obtained, an UPLC-MS/MS method was created and optimized to detect circumdatins in corn samples.

Initial Spore Density Has an Influence on Ochratoxin A Content in Aspergillus ochraceus CGMCC 3.4412 in PDB and Its Interaction with Seeds

The morphology and secondary metabolism of Aspergillus spp. are associated with initial spore density (ISD). Fatty acids (FA) are involved in the biosynthesis of aflatoxins (AF) through Aspergillus quorum sensing (QS). Here, we studied how ochratoxin A (OTA) was regulated by spore density in Aspergillus ochraceus CGMCC 3.4412. The results contribute to understanding the role of spore density in morphogenesis, OTA biosynthesis, and host-pathogen interactions. When A. ochraceus was grown in Potato Dextrose Broth (PDB) media at different spore densities (from 10¹ to 10⁶ spores/mL), more OTA was produced when ISD were increased, but a higher level of ISD inhibited OTA biosynthesis. Seed infection studies showed that peanuts (Arachis hypogaea) and soybeans (Glycine max) with high FA content were more susceptible to OTA production when infected by A. ochraceus and reactive oxygen species (ROS)-induced OTA biosynthesis. These results suggested that FA was vital for OTA biosynthesis, and that oxidative stress was closely related to OTA biosynthesis in A. ochraceus.

Development of a high-yielding bioprocess for 11-α hydroxylation of canrenone under conditions of oxygen-enriched air supply

A high yielding bioprocess for 11-α hydroxylation of canrenone (1a) using Aspergillus ochraceus ATCC 18500 was developed. The optimization of the biotransformation involved both fermentation (for achieving highly active mycelium of A. ochraceus) and biotransformation with the aim to obtain 11-α hydroxylation with high selectivity and yield. A medium based on sucrose as C-source resulted particularly suitable for conversion of canrenone into the corresponding 11-hydroxy derivative, whereas the use of O₂-enriched air and dimethyl sulfoxide (DMSO) as a co-solvent for increasing substrate solubility played a crucial role for obtaining high yields (>95%) of the desired product in high chemical purity starting from 30mM (10.2g/L) of substrate. The structure of the hydroxylated product was confirmed by a combination of two-dimensional NMR proton-proton correlation techniques.

Purification and characterisation of processive-type endoglucanase and β-glucosidase from Aspergillus ochraceus MTCC 1810 through saccharification of delignified coir pith to glucose

The study describes purification and characterisation of processive-type endoglucanase and β-glucosidase from Aspergillus ochraceus MTCC 1810 through bioconversion of delignified coir pith to fermentable glucose. The purified processive endoglucanase (AS-HT-Celuz A) and β-glucosidase (AS-HT-Celuz B) were found to have molecular mass of ≈78-kDa and 43-kDa respectively with optimum endoglucanase (35.63U/ml), total cellulase (28.15FPU/ml) and β-glucosidase (15.19U/ml) activities at 40°C/pH 6. The unique feature of AS-HT-Celuz A is the multiple substrate specificity and processivity towards both amorphous and crystalline cellulose. Zymogram indicated both endo and exoglucanase activities residing in different binding sites of a single protein exhibiting sequential synergy with its own β-glucosidase. Accordingly, the identified enzymes could be implemented as synergistic cellulases for complete cellulose saccharification which still considered an unresolved issue in bio-refineries.

Functional Characterization of New Polyketide Synthase Genes Involved in Ochratoxin A Biosynthesis in Aspergillus Ochraceus fc-1

Ochratoxin A (OTA), a potentially carcinogenic mycotoxin which contaminates grains, is produced by several Aspergillus species. A comparative sequence analysis of the OTA-producing Aspergillus ochraceus fc-1 strain and other Aspergillus species was performed. Two new OTA-related polyketide synthase (PKS) (AoOTApks) genes were identified. The predicted amino acid sequence of AoOTApks-1 displayed high similarity to previously identified PKSs from OTA-producing A. carbonarius ITEM 5010 (67%; [PI] No. 173482) and A. niger CBS 513.88 (62%; XP_001397313). However, the predicted amino acid sequence of AoOTApks-2 displayed lower homology with A. niger CBS 513.88 (38%) and A. carbonarius ITEM 5010 (28%). A phylogenetic analysis of the β-ketosynthase and acyl-transferase domains of the AoOTApks proteins indicated that they shared a common origin with other OTA-producing species, such as A. carbonarius, A. niger, and A. westerdijkiae. A real-time reverse-transcription PCR analysis showed that the expression of AoOTApks-1 and -2 was positively correlated with the OTA concentration. The pks gene deleted mutants ∆AoOTApks-1 and ∆AoOTApks-2 produced nil and lesser OTA than the wild-type strain, respectively. Our study suggests that AoOTApks-1 could be involved in OTA biosynthesis, while AoOTApks-2 might be indirectly involved in OTA production.

Efficiency of Artemisia nilagirica (Clarke) Pamp. essential oil as a mycotoxicant against postharvest mycobiota of table grapes

BACKGROUND

In order to get a potent botanical fungicide for the management of fungal decay of table grapes, an experiment was conducted in which 20 essential oils of higher plants were screened at 0.33 µL mL(-1) against dominant fungi causing decay of table grapes, including Aspergillus flavus, A. niger and A. ochraceus. Furthermore, the minimum inhibitory/fungicidal concentration, fungitoxic spectrum and mycotoxin inhibition activity of the most potent oil were determined. The efficacy of the most potent oil in preservation of table grapes, along with organoleptic evaluation, was also carried out by storing 1 kg of grapes in the oil vapour.

RESULTS

Artemisia nilagirica oil was found to be most toxic, exhibiting 100% mycelia inhibition of all test fungi. Moreover, 0.29 µL mL(-1) A. nilagirica oil was fungistatic and 0.58 µL mL(-1) was fungicidal for all tested species of Aspergillus. The oil exhibited a broad range of fungitoxicity against other grape berry-rotting fungi. Artemisia nilagirica oil completely suppressed the growth and mycotoxin (AFB1 and OTA) secretion of aflatoxigenic and ochratoxigenic strains of Aspergillus at 1.6 µL mL(-1) . During the in vivo experiment, fumigation of 1 kg of table grapes with 200 and 300 µL dosage of A. nilagirica oil enhanced the shelf life for up to 9 days. The oil did not show any phytotoxic effect. Besides, oil application did not substantively change the sensory properties of the fruits.

CONCLUSION

Artemisia nilagirica oil can be used as an alternative botanical fungicide for the control of fruit-rotting fungi of stored grapes.

Inhibitory effect of essential oils on Aspergillus ochraceus growth and ochratoxin A production

Ochratoxin A (OTA) is a mycotoxin which is a common contaminant in grains during storage. Aspergillus ochraceus is the most common producer of OTA. Essential oils play a crucial role as a biocontrol in the reduction of fungal contamination. Essential oils namely natural cinnamaldehyde, cinnamon oil, synthetic cinnamaldehyde, Litsea citrate oil, citral, eugenol, peppermint, eucalyptus, anise and camphor oils, were tested for their efficacy against A. ochraceus growth and OTA production by fumigation and contact assays. Natural cinnamaldehyde proved to be the most effective against A. ochraceus when compared to other oils. Complete fungal growth inhibition was obtained at 150-250 µL/L with fumigation and 250-500 µL/L with contact assays for cinnamon oil, natural and synthetic cinnamaldehyde, L. citrate oil and citral. Essential oils had an impact on the ergosterol biosynthesis and OTA production. Complete inhibition of ergosterol biosynthesis was observed at ≥ 100 µg/mL of natural cinnamaldehyde and at 200 µg/mL of citral, but total inhibition was not observed at 200 µg/mL of eugenol. But, citral and eugenol could inhibit the OTA production at ≥ 75 µg/mL and ≥ 150 µg/mL respectively, while natural cinnamaldehyde couldn't fully inhibit OTA production at ≤ 200 µg/mL. The inhibition of OTA by natural cinnamaldehyde is mainly due to the reduction in fungal biomass. However, citral and eugenol could significant inhibit the OTA biosynthetic pathway. Also, we observed that cinnamaldehyde was converted to cinnamic alcohol by A. ochraceus, suggesting that the antimicrobial activity of cinnamaldehyde was mainly attributed to its carbonyl aldehyde group. The study concludes that natural cinnamaldehyde, citral and eugenol could be potential biocontrol agents against OTA contamination in storage grains.

[Aspergillus ochraceus myxomycetes produce extracellular proteinases--protein C activators of blood plasma]

Natural isolates of Aspergillus ochraceus myxomycetes from soil and plant remains from various regions have been screened. The isolated strains were characterized by similar cultural and morphological features and an identical nucleotide sequence in the ITS1-5,8S-ITS2 region of rDNA. The ability of the extracellular proteinases of A. ochraceus myxomycetes to activate protein C of blood plasma has been established. Differences are revealed in the accumulation of proteinases activating protein C and proteinases with thrombin- and plasmin-like activities in the growth dynamics of producers.

Decolorization of adsorbed textile dyes by developed consortium of Pseudomonas sp. SUK1 and Aspergillus ochraceus NCIM-1146 under solid state fermentation

The objective of this study was to develop consortium using Pseudomonas sp. SUK1 and Aspergillus ochraceus NCIM-1146 to decolorize adsorbed dyes from textile effluent wastewater under solid state fermentation. Among various agricultural wastes rice bran showed dye adsorption up to 90, 62 and 80% from textile dye reactive navy blue HE2R (RNB HE2R) solution, mixture of textile dyes and textile industry wastewater, respectively. Pseudomonas sp. SUK1 and A. ochraceus NCIM-1146 showed 62 and 38% decolorization of RNB HE2R adsorbed on rice bran in 24h under solid state fermentation. However, the consortium of Pseudomonas sp. SUK1 and A. ochraceus NCIM-1146 (consortium-PA) showed 80% decolorization in 24h. The consortium-PA showed effective ADMI removal ratio of adsorbed dyes from textile industry wastewater (77%), mixture of textile dyes (82%) and chemical precipitate of textile dye effluent (CPTDE) (86%). Secretion of extracellular enzymes such as laccase, azoreductase, tyrosinase and NADH-DCIP reductase and their significant induction in the presence of adsorbed dye suggests their role in the decolorization of RNB HE2R. GCMS and HPLC analysis of product suggests the different fates of biodegradation of RNB HE2R when used Pseudomonas sp. SUK1, A. ochraceus NCIM-1146 and consortium PA.

[Effects of environmental stress on secondary metabolites of Aspergillus ochraceus LCJ11-102 associated with the coral Dichotella gemmacea]

OBJECTIVE

To explore the secondary metabolites of fungus Aspergillus ochraceus LCJ11-102 associated with the coral Dichotella gemmacea under environmental stress and to obtain characteristic compounds with biological activities.

METHODS

A nutrient-deprived culture medium (biomimetic culture) and a high salt culture medium were used for fermentation. Fingerprints of HPLC of the fermentation broth were used to investigate the diversity of secondary metabolites. Compounds were isolated by column chromatography on silica gel, Sephadex LH-20, and preparative HPLC. Their structures were identified by spectroscopic analyses and the modified Mosher's method.

RESULTS

Different secondary metabolites were produced by A. ochraceus LCJ11-102 under two different culture conditions. (R)-mellein (1), (5,6-trans, 8,9-threo-) -9-chloro-8-hydroxy-8, 9-deoxyaspyrone (2), (5,6-erythro-, 8,9-threo-) -9-chloro-8-hydroxy-8, 9-deoxyasperlactone (3), and (5S, 6R, 9S)-dihydroaspyrone (4) were identified from the biomimetic cultures, and R (+) -semi-vioxanthin (5) was identified from the high salt cultures, respectively.

CONCLUSION

Environmental stress obviously induces microbes to produce different secondary metabolites. And biomimetic culture is an effective approach to obtain active chloro compounds from marine microorganisms.

Pathological outcomes in kidney and brain in male Fischer rats given dietary ochratoxin A, commencing at one year of age

Malignant renal carcinoma, manifest in morbid ageing rats, is the striking component of an otherwise silent response after about nine months of exposure to ochratoxin A in the first year of life (daily intake ~100-250 µg/kg body weight). Reasons for the long latency are unclear, as is whether there would be a similar carcinogenic response if toxin exposure started at one year of age. Therefore, 24 male Fischer rats were given 100 µg ochratoxin A as a daily dietary contaminant for 35 weeks from age 50 weeks. Plasma ochratoxin A concentration reached a maximum value of ~8 µg/mL within one month of starting the toxin regimen. No renal carcinomas occurred. Four renal adenomas, two of which were only microscopic, were found among the six rats surviving for 110 weeks. The findings raise new questions about a difference between young adults and mature adults in sensitivity of male rats to the ochratoxin A-induced DNA damage necessary for renal carcinogenesis. A pilot histological study of perfuse-fixed brains of the toxin-treated rats showed no gross abnormalities, correlating with the consistent absence of behavioral or neurological disorders from chronic ochratoxin A exposure regimens in the range 100-250 µg/kg/day during the second half of life. Reasoned questioning concerning ochratoxin A as a neurotoxic mycotoxin is made.

Intracellular biogenic silver nanoparticles for the generation of carbon supported antiviral and sustained bactericidal agents

Intracellular silver nanoparticles produced by exposing silver ions to the fungus Aspergillus ochraceus were heat-treated in nitrogen environment to yield silver nanoparticles embedded in carbonaceous supports. This carbonaceous matrix embedded silver nanoparticles showed antimicrobial properties against both bacteria (Gram-positive and Gram-negative) and virus (M 13 phage virus). The bactericidal effects were noticed even after washing and repeated exposure of these carbon supported silver nanoparticles to fresh bacterial cultures, revealing their sustained activity.

Analysis of the effect of nutritional factors on OTA and OTB biosynthesis and polyketide synthase gene expression in Aspergillus ochraceus

The effect of a wide variety of nutritional based biotic factors on the production of both OTA and OTB biosynthesis in A. ochraceus was assessed. Different carbon sources including glucose, sucrose, maltose, galactose, xylose and glycerol appear to repress OTA production when the fungus is grown in OTA permissive PDY medium. In contrast lactose appears to induce OTA production, with the addition of lactose and galactose to the OTA restrictive PDC medium resulting in marked increases in OTA levels. The addition of lactose to MCB and PDY media considerably increases OTB production. The addition of both sucrose and galactose to MCB has similar yet less marked effects. Different nitrogen sources also affect OTA production with ammonium chloride significantly reducing OTA production, while organic nitrogen sources such as urea and amino acids including phenylalanine, lysine, glutamine and proline induce OTA production. The induction of otapksAo gene expression under these conditions correlates well with the levels of OTA produced under the same experimental conditions, suggesting that the observed effects appear to be modulated, at least in part, at the level of gene transcription. However while the levels of OTB produced in A. ochraceus also appear to be influenced by these nutritional based biotic factors, this appears to be regulated in a manner which is independent of otapksAo gene expression.

Biodegradation of kerosene by Aspergillus ochraceus NCIM-1146

The filamentous fungus Aspergillus ochraceus NCIM-1146 was found to degrade kerosene, when previously grown mycelium (96 h) was incubated in the broth containing kerosene. Higher levels of NADPH-DCIP reductase, aminopyrine N-demethylase and kerosene biodegradation activities were found to be present after the growth in potato dextrose broth for 96 h, when compared with the activities at different time intervals during the growth phase. NADPH was the preferred cofactor for enzyme activity, which was inhibited by CO, indicating cytochrome P450 mediated reactions. A significant increase in all the enzyme activities was observed when mycelium incubated for 18 h in mineral salts medium, containing cholesterol, camphor, naphthalene, 1,2-dimethoxybenzene, phenobarbital, n-hexane, kerosene or saffola oil as inducers. Acetaldehyde produced by alcohol dehydrogenase could be used as an indicator for the kerosene biodegradation.

Biodegradation of Reactive blue-25 by Aspergillus ochraceus NCIM-1146

The present study dealt with the decolorization and degradation of textile dye Reactive blue-25 (0.1gl(-1)) by mycelium of Aspergillus ochraceus NCIM-1146. Spectrophotometric and visual examinations showed that the decolorization was through fungal adsorption, followed by degradation. Shaking condition was found to be better for complete and faster adsorption (7h) and decolorization (20 days) of dye Reactive blue-25 (100mgl(-1)) as compared to static condition. Presence of glucose in medium showed faster adsorption (4h) and decolorization of dye from bound (7 days) mycelium. FTIR and GCMS analysis study revealed biodegradation of Reactive blue-25 into two metabolites phthalimide and di-isobutyl phthalate.

Detection and quantification of Aspergillus westerdijkiae in coffee beans based on selective amplification of β-tubulin gene by using real-time PCR

Aspergillus westerdijkiae is a new species of fungus that was recently dismembered from Aspergillus ochraceus taxon. Most isolates of A. westerdijkiae are able to produce large amounts of a mycotoxin called ochratoxin A (OA). OA has been found in food and beverages, such as coffee. A. westerdijkiae is very similar to A. ochraceus, and several isolates previously identified as A. ochraceus are now identified as A. westerdijkiae. By using sequences of the beta-tubulin gene, we analyzed several isolates from Brazilian coffee bean samples, previously identified as A. ochraceus, to compare with those of A. westerdijkiae. In fact, most (84%) were identified as A. westerdijkiae. Since this species consistently produces large amounts of OA, we developed a specific primer-pair for detecting and quantifying it in coffee beans by using real-time PCR. The primers Bt2Aw-F 5'TGATACCTTGGCGCTTGTGACG and Bt2Aw-R 5'CGGAAGCCTAAAAAATGAAGAG provided an amplicon of 347 bp in all A. westerdijkiae isolates, and no cross-reaction was observed using DNA from A. ochraceus. The sensitivity of real-time PCR was more than 100 times higher than the cfu technique.

Inhibition of ochratoxin A production and growth of Aspergillus species by phenolic antioxidant compounds

The phenolic antioxidants, gallic acid, vanillic acid, protocatechuic acid, 4-hydroxybenzoic acid, catechin, caffeic acid, and chlorogenic acid were studied for their effects on ochratoxin A (OTA) production and fungal growth of ochratoxigenic Aspergilli. Of the 12 strains tested, which included A. alliaceus, A. lanosus, A. ochraceus, A. albertensis, A. melleus, A. sulphureus, A. carbonarius, A. elegans, and A. sclerotiorum, the greatest inhibition of OTA production was seen in A. sulphureus, A. elegans, and A. lanosus. Vanillic acid and 4-hydroxybenzoic acid were the most inhibitory to both OTA production and growth of most of the strains tested. However, A. ochraceus was not inhibited by either compound, and A. carbonarius was not inhibited by vanillic acid. The effect of each compound on OTA production and growth differed among strains and generally was variable, suggesting that species-specific OTA production and response to phenolic compounds may be influenced by different ecological and developmental factors. In addition, inhibition of OTA production by antioxidant compounds may be useful in determining biosynthetic and regulatory genes involved in both OTA production and stress response in ochratoxigenic Aspergilli.

Chemical characterization and quantification of siderophores produced by marine and terrestrial aspergilli

Ten aspergilli (five each from marine and terrestrial habitats) were screened for siderophore production. All test isolates produced siderophores as indicated by a positive reaction in the FeCl(3) test, chrome azurol sulphonate assay, and chrome azurol sulphonate agar plate test. Further, the test isolates were compared for their siderophore production potential and chemical characteristics. Examination of the chemical nature of the siderophores revealed that all test isolates produced hydroxamate siderophores that were trihydroxamate hexadentates. Wide-spread occurrence of siderophores in marine isolates indicate their functional role in maintaining overall productivity of coastal waters. Among all test aspergilli, marine Aspergillus versicolor was found to be the largest siderophore producer (182.5 microg/mL desferrioxamine mesylate equivalent), least siderophore production was recorded in a marine strain of Aspergillus niger (3.5 microg/mL desferrioxamine mesylate equivalent).

Mycotoxin contamination of food in Europe: Early detection and prevention strategies

This paper reviews the early detection and prevention strategies which have been employed in Europe for the control of mycotoxin contamination of food in the context of a hazard analysis critical control point (HACCP) framework. The critical control points (CCPs) in the whole food chain where mycotoxins such as trichothecenes and ochratoxins are important have been identified. Ecological studies on the effect of environmental factors which are marginal for growth and mycotoxin production have been identified for Fusarium culmorum and F. graminearum (deoxynivlenol production), and for Penicillium verrucosum and Aspergillus ochraceus (ochratoxin production) in relation to cereal production and for A. carbonarius in relation to grapes and wine production (ochratoxin formation). To minimise the entry of these mycotoxins into the food chain, effective and rapid diagnostic tools are required to monitor the CCPs effectively. To this end the potential use of molecular imprinted polymers, lateral flow devices and molecular-based techniques for the rapid detection and quantification of the mycotoxigenic moulds or their toxins have also been developed.

Non-specificity of nutritional substrate for ochratoxin A production by isolates of Aspergillus ochraceus

Aspergillus ochraceus is an important contaminant of diverse substrates, such as cereals, coffee, grapes and derivates. This fungus produce a nephrotoxic metabolite, ochratoxin A (OTA), whose presence on food and feeds may be an important risk for animal and human health. The aim of this work was to evaluate the significance of the origin of A. ochraceus isolates on their OTA production patterns on different substrates (yeast extract sucrose (YES) broth, irradiated barley grains, irradiated green coffee beans and sterilized grapes) and under different environmental conditions. Results did not show a significant influence of the isolation source on OTA-production profiles by A. ochraceus isolates on several substrates, since the isolates which produced the highest OTA amounts in vitro (YES medium) were also the isolates with the highest OTA yields on the other substrates. Abiotic factors assayed (water activity, temperature and substrate) affected significantly OTA productions by A. ochraceus. Maximum OTA amounts were detected at 25 degrees C and 0.98 a(w) on all substrates tested. The highest OTA accumulations found on the different substrates were: green coffee beans (> 2 mg g(-1)), barley grains (approximately 1 mg g(-1)), YES medium (13.9 microg ml(-1)) and grape (approximately 3 ng g(-1)).

The effects of yeasts involved in the fermentation of Coffea arabica in East Africa on growth and ochratoxin A (OTA) production by Aspergillus ochraceus

The effects of Pichia anomala, Pichia kluyveri and Hanseniaspora uvarum predominant during coffee processing on growth of Aspergillus ochraceus and production of ochratoxin A (OTA) on malt extract agar (MEA) and on coffee agar (CA) were studied. The three yeasts were able to inhibit growth of A. ochraceus when co-cultured in MEA and CA. Growth inhibition was significantly higher on MEA than on CA. Furthermore, P. anomala and P. kluyveri were found to have a stronger effect on growth of A. ochraceus than H. uvarum. The three yeasts were able to prevent spore germination of A. ochraceus in yeast glucose peptone (MYGP) broth. In yeast-free supernatant of MYGP broth after an incubation period of 72 h, spores of A. ochraceus were able to germinate with very short germ tubes, but further development of the germ tubes was inhibited. The three yeasts decreased the pH of MYGP broth from 5.6 to a range of 4.4-4.7, which was found to have no effect on spore germination of A. ochraceus. P. anomala, P. kluyveri and H. uvarum were able to prevent production of OTA by A. ochraceus when co-cultured on MEA. On CA medium, P. anomala and P. kluyveri prevented A. ochraceus from producing OTA. H. uvarum did not affect production of OTA by A. ochraceus on CA medium.

Effect of the post-harvest processing procedure on OTA occurrence in artificially contaminated coffee

The purpose of this work was to study how the type of post-harvest process, i.e. natural preparation known as the dry method, and two wet processes, affected contamination and toxin production up to the green coffee stage. Batches were contaminated with ochratoxin A or with OTA-producing strains of Aspergillus ochraceus and Aspergillus niger. For OTA artificial contamination, hulling or husk removal caused a reduction of OTA. When A. ochraceus was inoculated at low level, its growth was hampered by indigenous mould flora contrary that observed with A. niger. The fungal counts and OTA assays showed that the best way of limiting the development and impact of contaminating toxigenic flora "from the field" was the physical wet method.

Circumdatin H, a new inhibitor of mitochondrial NADH oxidase, from Aspergillus ochraceus

Circumdatin H (1), a new alkaloid from the culture broth of Aspergillus ochraceus, has been isolated, together with a known circumdatin, circumdatin E (2) and other known compounds: flavacol (3) and stephacidin A (4). The structure of 1 was established on the basis of chemical and spectral evidence. All of these alkaloids showed biological activity as inhibitors of the mammalian mitochondrial respiratory chain.

PCR detection assays for the ochratoxin-producing Aspergillus carbonarius and Aspergillus ochraceus species

Two PCR assays have been developed to detect Aspergillus carbonarius and Aspergillus ochraceus, considered the main sources of ochratoxin A (OTA) contaminating commodities, particularly grapes, coffee and derivatives, in warm climates. The species specific primers have been designed on the basis of ITS (internal transcribed spacers of rDNA units) sequence comparisons obtained from Aspergillus strains and have been tested in a number of strains from different origins and hosts. These PCR assays, based on multi-copy sequences, are highly sensitive and specific and represent a good tool for an early detection of OTA-producing Aspergillus species and to prevent OTA entering the food chain.

Characterization and regulation of new secondary metabolites from Aspergillus ochraceus M18 obtained by UV mutagenesis

UV irradiation of Aspergillus ochraceus NRRL 3174 conidia led to stable mutations in ochratoxin and penicillic-acid pathways. These mutants, especially M18, produced an unexpectedly large number of new metabolites. Two new compounds were purified by TLC and HPLC and their chemical structures were determined. They are 2,10-dimethyl 4-hydroxy-6-oxo-4-undecen-7-yne (1) and 4-(3-methyl-2- butenyl) oxy 1-phenyl acetic acid (2). Compound 1 is very active against Gram-positive bacteria, such as Staphylococcus aureus and Bacillus subtilis, but inactive against Gram-negative bacteria, fungi, and yeasts. However, compound 2 has no antibiotic activity. The production of 1 was generally associated with growth, whereas that of compound 2 was dissociated from growth. The biosynthesis of these 2 metabolites was influenced by the sources of carbon and nitrogen.

Modelling of effects of water activity and temperature on germination and growth of ochratoxigenic isolates of on a green coffee-based medium

Influence of water activity (0.75-0.99 a(w)) and temperature (10, 20 and 30 degrees C) on germination and mycelial growth on green coffee extract agar medium of three ochratoxigenic isolates of Aspergillus ochraceus was studied. Optimal conditions for germination and growth were observed at 0.95-0.99 a(w) and 20-30 degrees C for the three isolates. Minimum a(w) level for germination was 0.80, and 0.85 for mycelial growth. At marginal a(w) and temperature levels assayed, the lag phases prior to germination increased and the growth rates showed a significant decrease in comparison with the optimal conditions. Data were modelled by a multiple linear regression (MLR) and response surface models were obtained. Germination and growth of A. ochraceus in green coffee beans could be prevented or at least inhibited to some extent by minimising the time that coffee beans are exposed to temperature and humidity conditions near to the optimum during processing and storage. This could be an empirical approach to predict the effects of water activity and temperature conditions on the development of ochratoxigenic isolates of A. ochraceus during handling and storage of green coffee.

Effect of water activity and temperature on mycelial growth and ochratoxin A production by isolates of Aspergillus ochraceus on irradiated green coffee beans

Aspergillus ochraceus as a fungal contaminant and ochratoxin A (OTA) producer plays an important role in coffee quality. Temperature and water activity (a(w)) significantly influence mycelial growth and OTA production by isolates of A. ochraceus on green coffee beans. Maximum mycelial growth was found at 30 degrees C and 0.95 to 0.99 a(w). A marked decrease in growth rate was observed when temperature and a(w) were reduced. At 0.80 a(w), mycelial growth occurred only at 30 and 20 degrees C for one isolate. Maximum OTA production was found at 20 degrees C and 0.99 a(w). At 10 degrees C, OTA was not produced, regardless of a(w). Similarly, no OTA was detected at 0.80 a(w). OTA production ranged from the limit of detection (40 ng g(-1) of green coffee) to 17,000 ng g(-1) of green coffee. Significant intraspecific differences in mycelial growth and OTA production were found. Primary data for lag phases prior to mycelial growth under the influence of temperature and a(w) were modelled by multiple linear regression, and the response surface plots were obtained.

Influence of volatile compounds produced by yeasts predominant during processing ofCoffea arabica in East Africa on growth and ochratoxin A (OTA) production byAspergillus ochraceus

The effects of volatile compounds produced during coffee processing by Pichia anomala, P. kluyveri and Hanseniaspora uvarum on growth of Aspergillus ochraceus and production of ochratoxin A (OTA) were studied. On malt extract agar (MEA) and on coffee agar (CA), exposure of A. ochraceus to the gaseous phase of malt yeast glucose peptone (MYGP) plates inoculated with P. anomala, P. kluyveri and H. uvarum inhibited fungal growth, with the two Pichia spp. showing the strongest effect. The main esters and alcohols produced by the three yeasts were ethyl acetate, isobutyl acetate, 2-phenyl ethyl acetate, ethyl propionate and isoamyl alcohol. The individual esters and alcohols were found to affect fungal growth. The most effective compound in inhibiting fungal growth was 2-phenyl ethyl acetate; which at 48 microg/l headspace completely inhibited growth of A. ochraceus. Exposure of A. ochraceus to the gaseous phase of MYGP plates inoculated with P. anomala, P. kluyveri and H. uvarum prevented production of OTA. On CA medium, only the headspace of P. anomala and P. kluyveri prevented OTA production. Furthermore, when A. ochraceus was exposed to the headspace of the individual volatile compounds, 2-phenyl ethyl acetate was the most effective in preventing OTA production. Prevention of OTA seems to be due to reduction of fungal biomass.

Prediction of fungal growth and ochratoxin A production by Aspergillus ochraceus on irradiated barley grain as influenced by temperature and water activity

Ochratoxin A (OTA) is a secondary metabolite of Aspergillus and Penicillium species, including Aspergillus ochraceus, a species that can be found in stored cereal grains such as barley. The objective of this study was to determine the effects of water activity (a(w), 0.80-0.99), temperature (10, 20, 30 degrees C), and A. ochraceus isolate differences on radial growth and OTA production in irradiated barley grains. The three isolates showed optimal conditions for growth and ochratoxin A production at 0.99 a(w) and 30 degrees C, with a marked decrease of growth rates and OTA production at the lowest levels of a(w) and temperature assayed. The minimum a(w) level for growth, observed in this study, was 0.85 and 0.90 a(w) for OTA production. Significant differences among the isolates were found. Lag phases prior to fungal growth and OTA production values were modelled by multiple linear regression and response surface models. These models could provide an approximate prediction of growth and OTA production.

A polyketide synthase gene required for ochratoxin A biosynthesis in Aspergillus ochraceus

Ochratoxin A is an important nephrotoxic and nephrocarcinogenic mycotoxin, produced by Aspergillus ochraceus as a polyketide-derived secondary metabolite. A portion of a putative polyketide synthase gene (pks) involved in the biosynthesis of this mycotoxin was cloned by using a suppression subtractive hybridization PCR-based approach. The predicted amino acid sequence of the 1.4 kb clone shared 28-35 % identity to acyl transferase regions from fungal polyketide synthases found in the databases. Based on reverse transcription PCR studies, the pks gene is expressed only under ochratoxin A permissive conditions and only during the early stages of the mycotoxin synthesis. A mutant in which the pks gene has been interrupted cannot synthesize ochratoxin A. This report is the first of the cloning and characterization of a gene involved in ochratoxin A biosynthesis.

Bee Pollen, a Substrate that Stimulates Ochratoxin A Production by Aspergillus ochraceus Wilh

The capacity of bee pollen as a substrate for production of ochratoxin A (OTA) by a strain of Aspergillus ochraceus was studied. For control purposes corn, wheat and rice grains, and eleven liquid media were assayed. They were Yeast Extract Sucrose broth (YES), YES supplemented with 0.05, 0.1, 0.5, 1 and 5% bee pollen, YES supplemented with 0.5% peptone, 50% must, Wickerham medium, Aflatoxin Production medium and Coconut Broth Medium. Cultures were maintained at 28 degrees C for 4 weeks and were analyzed every seven days for OTA by liquid chromatography with fluorescence detection. OTA production in bee pollen was significantly (P < 0.01) higher than production in corn, wheat and rice grains regardless of incubation time. With regard to liquid cultures, OTA accumulation in YES supplemented with 5% bee pollen was significantly higher than in pollen-free liquid cultures. A positive correlation between the proportion of pollen added to YES medium and OTA level was observed. This is the first report concerning the use of bee pollen as a substrate to stimulate OTA production. On the basis of the preliminary results obtained in this study it can be hypothesized that bee pollen may constitute an important risk factor concerning the presence of OTA in the diet of consumers of that nutritious food.

Spoilage fungi and their mycotoxins in commercially marketed chestnuts

A nationwide survey was carried out to assess mould spoilage of Castanea sativa nuts sold in Canadian grocery stores in 1998-99. Morphological and cultural characters, along with secondary metabolite profiles derived from thin-layer chromatography, were used to sort and identify fungi cultured from nut tissue. Three mycotoxigenic fungi dominated (Penicillium crustosum, Penicillium glabrum/spinulosum and Penicillium discolor) and were isolated at frequencies of 67.1%, 18.6% and 17.7%, respectively, from a total sample size of 350 nuts. Another mycotoxin producer, Aspergillus ochraceus was also isolated, but at a much lower frequency. HPLC and diode array detection were used to confirm the suspected presence of the mycotoxins penitrem A, chaetoglobosin A and C, emodin and ochratoxin A in extracts prepared from naturally infected nut tissue. To the best of our knowledge, this is the first time emodin has been found in a naturally contaminated food source.

[Ochratoxin A and human health]

Ochratoxin A (OA) is produced mainly by Penicillium verrucosum, Aspergillus ochraceus and A. carbonarius and it was found as a contaminant in the large number of agricultural commodities, feedstuffs and animal organs such as kidney and liver of pig. Toxicological studies indicated that OA is a teratogenic, mutagenic and carcinogenic mycotoxin with the strong toxic effects on liver and kidney. In some endemic areas in the world, OA was suspected to be related to swine nephropathy and has been detected in blood samples from inhabitants in these areas as well. More and more attention was paid to the relationship between the consumption of food contaminated with OA and human health. In this paper, OA--producing fungi, the contamination of it to the agricultural commodities, its toxicity and risk assessment are reviewed.

Ochratoxin production by the Aspergillus ochraceus group and Aspergillus alliaceus

Ochratoxin A is a toxic and carcinogenic fungal secondary metabolite; its presence in foods is increasingly regulated. Various fungi are known to produce ochratoxins, but it is not known which species produce ochratoxins consistently and which species cause ochratoxin contamination of various crops. We isolated fungi in the Aspergillus ochraceus group (section Circumdati) and Aspergillus alliaceus from tree nut orchards, nuts, and figs in California. A total of 72 isolates were grown in potato dextrose broth and yeast extract-sucrose broth for 10 days at 30 degrees C and tested for production of ochratoxin A in vitro by high-pressure liquid chromatography. Among isolates from California figs, tree nuts, and orchards, A. ochraceus and Aspergillus melleus were the most common species. No field isolates of A. ochraceus or A. melleus produced ochratoxin A above the level of detection (0.01 microg/ml). All A. alliaceus isolates produced ochratoxin A, up to 30 microg/ml. We examined 50,000 figs for fungal infections and measured ochratoxin content in figs with visible fungal colonies. Pooled figs infected with A. alliaceus contained ochratoxin A, figs infected with the A. ochraceus group had little or none, and figs infected with Penicillium had none. These results suggest that the little-known species A. alliaceus is an important ochratoxin-producing fungus in California and that it may be responsible for the ochratoxin contamination occasionally observed in figs.

Experimental one year ochratoxin A toxicosis in pigs

Mild mycotoxic nephropathy was induced in 6 pigs by a diet containing ochratoxin A at 800 ppb, several times higher than that naturally encountered in some feed for pig production in Bulgaria. The nephropathy was expressed only as slightly hypertrophied kidneys with a faintly mottled surface, discernible at the end of the experiment to a skilled observer but probably not recognisable in routine slaughterhouse processing. Histological examination showed two types of changes: degenerative - affecting epithelial cells in some proximal tubules of pigs after 6 months, and proliferative changes in the interstitium which predominated after 1 year of exposure to ochratoxin A. Telangiectasis and lymph stasis were rarely seen. The renal lesions were similar to those described for classical mycotoxic porcine nephropathy formerly encountered in Denmark, but they were rather different from the porcine nephropathy which occurs spontaneously in Bulgaria. Measurement of ochratoxin A in serum provided analytical values complementary to feed intake and with similar concentration values. It also showed both accumulation with time, from 3 months to 6 months (approximately 1 ppm), and a 2-fold range of values within a group eating from a common feed source, as in commercial pig production. Mild symptomatology in this long, single-mycotoxin experiment serves to lessen somewhat the current perception of the direct renal toxicity of ochratoxin A alone, though a role in multi-toxin contexts is unquestioned.

Control of amylase production and growth characteristics of Aspergillus ochraceus

The growth and the extracellular amylase production by Aspergillus ochraceus were studied in a stationary culture medium. Maximum growth rate of this fungus was found after 5 days of incubation at 30 degrees C, but maximum amylase production was obtained after 2 days. The highest amylase production were attained with lactose, maltose, xylose and starch as carbon sources. The extracellular amylase production and mycelial growth were influenced by the concentration of starch. Other carbohydrates supported growth but did not induce amylase synthesis and glucose repressed it, indicating catabolite repression in this microorganism. The presence of both mechanisms of induction and repression suggests that at least these multiple forms of regulation are present in A. ochraceus. Of the nitrogen sources tested, casaminoacids, ammonium nitrate and sodium nitrate stimulated the highest yield of amylase. Optimal amylase production was obtained at pH 5.0, but enzyme activity was found only in the 4.0-6.0 pH range. These results were probably due to the inhibitory effect of NH4(+)-N in the culture medium.

A new antibiotic CJ-17,665 from Aspergillus ochraceus

A new antibiotic, CJ-17,665 (I) was isolated from the fermentation broth of Aspergillus ochraceus, CL41582. It inhibits growth of multi-drug resistant Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis, with MICs of 12.5, 12.5 and 25 microg/ml, respectively. The structure contains a diketopiperazine and an indole N-oxide moiety that is unusual in natural products.

Biosynthesis of ochratoxins by Aspergillus ochraceus

Shaken liquid fermentation of an isolate of Aspergillus ochraceus showed growth-associated production of ochratoxins A and B, followed by production of a related polyketide diaporthin. Later, between 150 and 250 h, mellein accumulated transitorily. In contrast, shaken solid substrate (shredded wheat) fermentation over 14 days produced mainly ochratoxins A and B (ratio ca. 5:1) in very high yield (up to 10 mg/g). In these systems experiments with 14C-labelled precursors and putative intermediates revealed temporal separation of early and late stages of the ochratoxin biosynthetic pathway, but did not support an intermediary role for mellein. The pentaketide intermediate ochratoxin beta was biotransformed very efficiently into both ochratoxins A and B, 14 and 19%, respectively. The already chlorinated ochratoxin alpha was only biotransformed significantly (4.85%) into ochratoxin A, indicating that chlorination is mainly a penultimate biosynthetic step in the biosynthesis of ochratoxin A. This was supported by poor (1.5%) conversion of radiolabelled ochratoxin B into ochratoxin A. Experiments implied that some ochratoxin B may arise by dechlorination of ochratoxin A.

Experimental mycotoxic nephropathy in pigs provoked by a diet containing ochratoxin A and penicillic acid

Mycotoxic nephropathy was induced in 18 young pigs by diets contaminated with strains of Aspergillus ochraceus containing ochratoxin A (OTA) and penicillic acid (PA) at levels corresponding to those naturally encountered in animal feeds in Bulgaria. Haematological and biochemical parameters, as well as the morphological and ultrastructural changes in various internal organs, and especially in the kidneys, were examined at different stages of development of the disease. A mottled surface of the kidneys was only seen in pigs exposed to a mouldy diet containing 180 ppb OTA for 3 months, but microscopic lesions, as well as changes in various haematological and biochemical parameters, were observed in all groups exposed to the same mouldy diet containing only 90 or 180 ppb OTA. Histological examination showed two types of change: degenerative changes affecting the epithelial cells of the proximal tubules, which predominated at the initial stage, and proliferative changes in the interstitium, which predominated at the later stage of the disease. Telangiectasis and lymph stasis were also seen, as well as degenerative changes in the capillary endothelium. The characteristic renal lesions were similar to those observed in spontaneous cases of mycotoxic porcine nephropathy in Bulgaria, but they were a little different from the classic Danish porcine nephropathy. The enhanced toxicity of OTA in our study may be due to a synergistic effect between OTA and PA or to some other unknown metabolites produced by the same ochratoxinogenic strains of A. ochraceus.

Impact of environment and interspecific interactions between spoilage fungi and Aspergillus ochraceus on growth and ochratoxin production in maize grain

Using layers of irradiated but still fertile maize grain, the effects of water activity (0.995, 0.95 a(w)) and temperature (18, 30 degrees C) on interspecific interactions between Aspergillus ochraceus and five other spoilage fungi were examined. Asp. ochraceus was not competitive against Asp. flavus, Asp. niger, or Alternaria alternata at 18 degrees C when water was freely available (0.995 a(w)), while at 0.95 a(w) it was dominant against Asp. candidus, Asp. flavus and Alt. alternata. At 30 degrees C and 0.995 a(w), Asp. ochraceus was dominated by other fungi, except Alt. alternata, and was mutually antagonistic to Asp. candidus and Eurotium amstelodami. However, at 30 degreees C and 0.95 a(w), it was competitive against Asp. candidus and Alt. alternata, but not against the other species examined. The overall Index of Dominance showed that Asp. ochraceus was not competitive under the conditions examined here. At 18 degrees C ochratoxin production by Asp. ochraceus was inhibited significantly by Asp. candidus (0.995 and 0.95 a(w)) and Asp. niger (0.995 a(w)). When grown on maize grain at 30 degrees C, ochratoxin production by Asp. ochraceus was significantly inhibited by other spoilage fungi when both were grown on maize grain, especially by Asp. niger and E. amstelodami (0.995 a(w)) and Asp. flavus at 0.95 a(w). These results suggest that, to a large extent, A. ochraceus is not as competitive as some other spoilage fungi in primary resource capture on maize grain at a(w) of 0.95 or above, although it may modify resource quality and influence secondary colonisation by other species under the conditions tested.

Ochratoxin formation in Aspergillus ochraceus with particular reference to spoilage of coffee

Production of ochratoxin on media by eight isolates of Aspergillus ochraceus from coffee or its processing environment in India, Indonesia, Kenya, and Brazil, and seven Brazilian isolates from other commodities, has been compared with yields in shaken fermentation on shredded wheat and coffee (Coffea arabica). Shredded wheat most consistently allowed expression of biosynthesis of ochratoxins A and B in yields up to 3.5% of the dry product. Culture on artificial media was an unreliable predictor of ochratoxin yield on both shredded wheat and coffee. Coffee was a relatively poor substrate for ochratoxin production particularly when sterilised. Notably, two Asian coffee isolates produced 400 mg kg(-1) ochratoxin A on unsterilised ground green coffee, showing this to be a preferred substrate for further experimentation. The study focused on isolates of A. ochraceus, which from evidence of culture on media would not be expected to be suitable fungi for future studies to establish both the fact of spoilage of coffee by A. ochraceus and the dynamics of ochratoxin formation by isolates of this species.

Influence of halogen salts on the production of the ochratoxins by Aspergillus ochraceus Wilh

The first report of the biological production of bromo ochratoxin B by Aspergillus ochraceus Wilh. is presented as well as a study of the influence of potassium bromide, potassium iodide, potassium fluoride, and potassium chloride on the production of ochratoxin A and ochratoxin B. Potassium fluoride and potassium iodide inhibited the growth of the fungus, whereas potassium chloride substantially stimulated the production of ochratoxin A in shaken solid substrate fermentation on whole wheat or shredded wheat, generally giving a high yield of ochratoxins. Increasing levels of potassium bromide led to a decline in ochratoxin A production and an increase in bromo-ochratoxin B, ochratoxin B, and 4-hydroxy ochratoxin B. Nevertheless, A. ochraceus was much less versatile in the bromo analogues than other fungi, which produce metabolites containing chlorine. Analysis included aminopropyl solid-phase extraction column cleanup followed by quantitative analysis on reversed-phase HPLC using fluorescence detection and employing N-(5-chloro-2-hydroxybenzoyl)phenylalanine as an internal standard.