A new antibiotic CJ-17,665 from Aspergillus ochraceus. (1/15)

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.  (+info)

Ochratoxin production by the Aspergillus ochraceus group and Aspergillus alliaceus. (2/15)

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.  (+info)

Bilirubin dehydrogenase, an enzyme in Aspergillus ochraceus IB-3 useful for diagnostic measurement of bilirubin. (3/15)

Bilirubin dehydrogenase, a membrane-bound enzyme that catalyzes the one-step oxidation of ditaurobilirubin and bilirubin to ditaurobiliverdin and biliverdin, respectively, in the presence of an electron acceptor, was found in Aspergillus ochraceus IB-3, and purified from the membrane fraction through solubilization by Triton X-100. Phenazine and quinone derivatives acted as electron acceptors. Accumulation of ditaurobiliverdin and biliverdin by enzyme catalysis increased the absorbance at 660 nm, which is far from the range of wavelengths affected by serum ingredients. The enzyme selectively oxidized ditaurobilirubin at low pH, so changes in the reaction pH enable the enzyme to discriminate between the bilirubin fractions ditaurobilirubin (an example of conjugated bilirubin) and bilirubin (an example of unconjugated bilirubin). Using the enzyme, 2 to 80 microM of ditaurobilirubin were measured accurately by monitoring the changes in absorbance at 660 nm.  (+info)

A polyketide synthase gene required for ochratoxin A biosynthesis in Aspergillus ochraceus. (4/15)

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.  (+info)

Variants of Aspergillus alutaceus var. alutaceus (formerly Aspergillus ochraceus) with altered ochratoxin A production. (5/15)

The present studies, using Aspergillus alutaceus var. alutaceus Berkeley et Curtis (formerly A. ochraceus Wilhelm) NRRL 3174 along with three other wild-type strains, were undertaken in an attempt to understand the effects of irradiation and other treatments on mycotoxin production in grain. Bedford barley was inoculated with spores of NRRL 3174, gamma irradiated, and incubated at 28 degrees C and 25% moisture. After 10 days of incubation, two colony types, ochre (parental) and yellow (variant), were isolated from the grain. Further culturing of the yellow variant resulted in the spontaneous appearance of a white variant that exhibited greatly enhanced fluorescence under UV light. In subsequent work, we have also isolated variants producing a soluble red pigment. In addition, in model experiments involving irradiation (1 kGy) of pure cultures, induction frequencies ranging between 2 and 4% (survival basis) were observed for the yellow and red variants. Inoculation of these variants into wheat and incubation for 14 days at 28 degrees C and 32% moisture resulted in ochratoxin A production in the relative amounts of 0.09:1:4.6:9.3 for the red, ochre (parental), yellow, and white variants, respectively. Additional characteristics of these isolates are described. Confirmation that the white high-ochratoxin-A-producing variants were derived from the parental strain was demonstrated by obtaining revertant sectors in monoclonal cultures of the variants.  (+info)

Role of the competitive microbial flora in the radiation-induced enhancement of ochratoxin production by Aspergillus alutaceus var. alutaceus NRRL 3174. (6/15)

The radiation sensitivity and the toxigenic potential of conidiospores of the fungus Aspergillus alutaceus var. alutaceus were determined after irradiation with 60Co gamma rays and high-energy electrons. Over the pH range of 3.6 to 8.8, the doses required for a 1 log10 reduction in viability based on the exponential portion of the survival curve ranged from 0.21 to 0.22 kGy, with extrapolation numbers (extrapolation of the exponential portion of the survival curve to zero dose) of 1.01 to 1.33, for electron irradiation, and from 0.24 to 0.27 kGy, with extrapolation numbers of 2.26 to 5.13, for gamma irradiation. Nonsterile barley that was inoculated with conidia of the fungus and then irradiated with either electrons or gamma rays and incubated for prolonged periods at 28 degrees C and at a moisture content of 25% produced less ochratoxin A with increasing doses of radiation. Inoculation of barley following irradiation resulted in enhanced ochratoxin levels compared with unirradiated controls. In these experiments, inoculation with 10(2) spores per g produced greater radiation-induced enhancement than inoculation with 10(5) spores per g. There was no radiation-induced enhancement when the barley was surface sterilized by chemical means prior to irradiation. These results are consistent with the hypothesis that a reduction in the competing microbial flora by irradiation is responsible for the enhanced mycotoxin production observed when nonsterile barley is inoculated with the toxigenic fungus A. alutaceus var. alutaceus after irradiation.  (+info)

Characterization of alcohol oxidase from Aspergillus ochraceus AIU 031. (7/15)

An alcohol oxidase (AOD) was found from Aspergillus ochraceus AIU 031, and its characteristics were revealed. This enzyme oxidized short-chain primary alcohols and ethylene glycol, and belonged to the same group as AOD from methylotrophic yeast. However, it differed in the following properties. The K(m) value for ethanol was larger and that for ethylene glycol was smaller than those of AODs derived from methylotrophic yeasts. The ethanol oxidation was optimal at pH 5-7 and 50-55 degrees C. The molecular mass of this enzyme was 262 kDa and consisted of four identical subunits of 68 kDa, which were much smaller than those of methylotrophic yeasts.  (+info)

Identification of the antimicrobial substances produced by Solanum palinacanthum (Solanaceae). (8/15)

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