Virulence Composition of Phytophthora sojae in Michigan.

Knowing the virulence composition of Phytophthora sojae is important for the management of Phytophthora root and stem rot of soybean. Plant samples were collected in Michigan from diseased plants in soybean fields with Phytophthora root and stem rot symptoms. Eighty-seven isolates of P. sojae were evaluated for virulence using 13 differential soybean cultivars. Rps 3b, 3a, 1b, 1k, and 6 were resistant to 81, 77, 74, 69, and 66% of the isolates, respectively, while Rps 1a and 7 were resistant to only 12 to 13% of the isolates. Races 2, 25, 41, and 44 of P. sojae were identified among the isolates and reported for the first time in Michigan. Virulence formulae of 69 isolates did not match those of currently known races of P. sojae. Nine isolates were considered nonpathogenic. Incorporating Rps genes 1b, 1k, 3a, 3b, and 6 in soybean cultivars with good field tolerance, in conjunction with other control measures, should offer improved protection of soybeans from Phytophthora root and stem rot in Michigan.

Expression of a functional antizearalenone single-chain Fv antibody in transgenic Arabidopsis plants.

The efficacy of cloning a recombinant mycotoxin antibody in plants was tested using Arabidopsis as a model. An antizearalenone single-chain Fv (scFv) DNA fragment was first cloned in the newly constructed phage display vector (pEY.5) and then recloned in the plant transformation vector pKYLX71::35S(2). After transformation, constructs of antizearalenone scFv were introduced into immature Arabidopsis seeds via Agrobacterium tumefaciens mediation by vacuum infiltration. Only plants transformed with the construct containing a PR-1b signal peptide sequence produced transgenic offspring. The antizearalenone scFv "plantibody" from these transgenic plants bound zearalenone with a high affinity (50% inhibitory concentration, 11.2 ng/ml) that was comparable to that of bacterially produced scFv antibody and the parent monoclonal antibody (MAb). By electron microscopic immunogold labeling, the presence of antizearalenone scFv was detected mainly in the cytoplasm and only occasionally outside the cell. Like bacterially produced scFv antibody, antizearalenone scFv plantibody exhibited greater sensitivity to methanol destabilization than did the parent MAb. The sensitivity of antizearalenone scFv plantibody to acidic disassociation was similar to the sensitivities of bacterially produced scFv antibody and MAb. Expression of specific plantibodies in crops might be useful for neutralizing mycotoxins in animal feeds and for reducing mycotoxin-associated plant diseases.

Identification of mimotope peptides which bind to the mycotoxin deoxynivalenol-specific monoclonal antibody.

Monoclonal antibody 6F5 (mAb 6F5), which recognizes the mycotoxin deoxynivalenol (DON) (vomitoxin), was used to select for peptides that mimic the mycotoxin by employing a library of filamentous phages that have random 7-mer peptides on their surfaces. Two phage clones selected from the random peptide phage-displayed library coded for the amino acid sequences SWGPFPF and SWGPLPF. These clones were designated DONPEP.2 and DONPEP.12, respectively. The results of a competitive enzyme-linked immunosorbent assay (ELISA) suggested that the two phage displayed peptides bound to mAb 6F5 specifically at the DON binding site. The amino acid sequence of DONPEP.2 plus a structurally flexible linker at the C terminus (SWGPFPFGGGSC) was synthesized and tested to determine its ability to bind to mAb 6F5. This synthetic peptide (designated peptide C430) and DON competed with each other for mAb 6F5 binding. When translationally fused with bacterial alkaline phosphatase, DONPEP.2 bound specifically to mAb 6F5, while the fusion protein retained alkaline phosphatase activity. The potential of using DONPEP.2 as an immunochemical reagent in a DON immunoassay was evaluated with a DON-spiked wheat extract. When peptide C430 was conjugated to bovine serum albumin, it elicited antibody specific to peptide C430 but not to DON in both mice and rabbits. In an in vitro translation system containing rabbit reticulocyte lysate, synthetic peptide C430 did not inhibit protein synthesis but did show antagonism toward DON-induced protein synthesis inhibition. These data suggest that the peptides selected in this study bind to mAb 6F5 and that peptide C430 binds to ribosomes at the same sites as DON.

Comparison of gas chromatography-electron capture and enzyme-linked immunosorbent assay for deoxynivalenol in milled fractions of naturally contaminated wheat.

An enzyme-linked immunosorbent assay (ELISA) for deoxynivalenol was compared with a gas chromatography-electron capture assay to determine deoxynivalenol levels in milled fractions of wheat. The milling provided eight fractions: first, second, and third break flours; first, second, and third reduction flours; brans; and shorts. The difference between levels of deoxynivalenol quantitated by ELISA or gas chromatography did not depend significantly on the wheat samples or milled wheat fractions. For none of the fractions or samples did the differences differ significantly (P=0.05) from zero. Based on these comparative tests, ELISAs for deoxynivalenol in milled wheat fractions should provide reliable results rapidly and economically in a commercial setting.

Variability of Vomitoxin in Truckloads of Wheat in a Wheat Scab Epidemic Year.

Wheat scab, caused by Gibberella zeae, has been a serious disease in parts of the Midwest. One factor contributing to the importance of wheat scab is the contamination of grain by the mycotoxin vomitoxin (deoxynivalenol, DON), a toxic secondary metabolite. The U.S. Food and Drug Administration advisory levels for vomitoxin in wheat and wheat products require an accurate and precise assessment of vomitoxin concentration. In this study, randomly collecting probes of wheat from individual trucks and analyzing the ground wheat from each probe produced significantly less variability than subsampling and analyzing 50 g of whole kernels from the probes. The variability introduced by subsampling the probes and analyzing 50 g of whole kernels affects the precision and confidence of vomitoxin estimates. Tables of confidence intervals were developed for different sampling and subsampling patterns. To be 95% certain that the true vomitoxin concentration does not exceed the sample estimate by 1 µg/g, analyzing either four individual probes or 5-12% subsamples of these probes would be sufficient. To increase the accuracy to about 0.5 µg/g, either an analysis of seven probes or a 5-12% subsample of 10 probes would be necessary, based on a one-sided confidence interval.

Molecular cloning, expression, and characterization of a functional single-chain Fv antibody to the mycotoxin zearalenone.

The heavy-chain and kappa light-chain variable region genes of an antizearalenone hybridoma cell line (2G3-6E3-2E2) were isolated by PCR and joined by a DNA linker encoding peptide (Gly4Ser)3 as a single-chain Fv (scFv) DNA fragment. The scFv DNA fragment was cloned into a phagemid (pCANTAB5E) and expressed as a fusion protein with E tag and phage M13 p3 in Escherichia coli TG1. In the presence of helper phage M13K07, the scFv fusion protein was displayed on the surfaces of recombinant phages. High-affinity scFv phages were enriched through affinity selection in microtiter wells coated with zearalenone-ovalbumin conjugate. The selected recombinant phages were used to infect E. coli HB2151 for the production of soluble scFv antibodies. One selected clone (pQY1.5) in HB2151 secreted a soluble scFv antibody (QY1.5) with a high zearalenone-binding affinity (concentration required for 50% inhibition of binding, 14 ng/ml), similar to that of parent monoclonal antibody in a competitive indirect enzyme-linked immunosorbent assay. However, scFv QY1.5 exhibited higher cross-reactivity with zearalenone analogs and had greater sensitivity to methanol destabilization than the parent monoclonal antibody did. Nucleotide sequence analyses revealed that the light-chain portion of scFv QY1.5 had a nucleotide sequence identity of 97% to a mouse germ line gene VK23.32 in mouse kappa light-chain variable region subgroup V, whereas the heavy-chain nucleotide sequence was classified as mouse heavy-chain subgroup III (D) but without any closely related members having highly homologous complementarity-determining region sequences. The potential of soluble scFv QY1.5 for routine screening of zearalenone and its analogs was demonstrated with zearalenone-spiked corn extracts.

Density Gradient Study of Victorin-Binding Proteins in Oat (Avena sativa) Cells.

Victorin-binding proteins (VBPs) in oat (Avena sativa) cells were identified using native victorin and anti-victorin polyclonal antibodies. Homogenates of oat tissues were fractionated in continuous or discontinuous sucrose density gradients or with an aqueous two-phase method, and covalent binding sites of victorin were detected by western blotting. In a 20 to 45% (w/w) sucrose continuous density gradient, the 100-kD VBP was located in fractions of 37 to 44% sucrose, with a peak at 39% sucrose. Based on marker enzyme assays, plasma membranes peaked at 39 to 41% sucrose, mitochondria peaked at 41%, but Golgi and endoplasmic reticulum were in lower density fractions, peaking at 28 to 29% and 22 to 24% sucrose, respectively. The 100-kD VBP was not found in plasma membranes purified by the aqueous two-phase method or in mitochondria purified by discontinuous density gradient centrifugation. Victorin binding to 65- and 45-kD proteins was detected in all fractions in the continuous sucrose density gradients. The 65- and 45-kD proteins were both detected in purified plasma membranes, but only the 65-kD protein was detected in purified mitochondria. The subcellular location of VBPs was the same in sensitive and resistant oat cells.

Covalent binding sites of victorin in oat leaf tissues detected by anti-victorin polyclonal antibodies.

Polyclonal antibodies against victorin, the host-specific toxin produced by Cochliobolus victoriae, were raised in rabbits immunized with a victorin-bovine serum albumin conjugate. The antibodies were purified from serum by protein A column chromatography and characterized by indirect and direct enzymelinked immunosorbent assays (ELISA). The concentration of victorin that inhibited anti-victorin antibody binding by 50% was 10 nanograms per milliliter in an indirect ELISA. The lowest concentration of victorin detectable was 10 picograms per milliliter. In a direct ELISA, 25 nanograms per milliliter of victorin inhibited binding of victorin-horseradish peroxidase conjugate by 50%. In vivo and in vitro covalent binding of victorin to proteins in susceptible and resistant oat (Avena sativa) tissue was examined by western blotting assays using anti-victorin antibody and a second antibody conjugated with (125)I or alkaline phosphatase. In vivo binding of victorin to proteins of 100 and 45 kilodaltons was observed in both susceptible and resistant cultivars of oats. Victorin also bound in vitro to proteins of 100, 65, and 45 kilodaltons in both susceptible and resistant oats. The data indicate that victorin binds covalently to the same sites in susceptible and resistant genotypes of oats.

Lifetime evidence for a weak lowest electronic transition in adenosine.

The fluorescence decay of adenosine in 1:1 glycol/water glass has been determined at 77K using narrow pulse (700 ps) laser excitation at 290 nm and fluorescence detection with a scanned narrow-gate (100 ps) fast sampler together with digital averaging. Data analysis by re-iterative non-linear least squares convolution shows the decay is best represented by the bi-exponential form I(t) = 0.59exp - t/1.2ns + 0.41 exp - t/7.0ns. This leads to intrinsic radiative lifetimes of 150 ns and 220 ns respectively and a combined oscillator strength of 1.5 x 10(-2). Compared with the overall oscillator strength of 0.29 for the entire first absorption band of adenosine this indicates that transitions to and from the lowest-lying state in this band are quite forbidden. This is not accounted for by current theoretical considerations.

Enzyme-linked immunosorbent assay for screening aflatoxin B1 in cottonseed products and mixed feed: collaborative study.

A joint AOAC/IUPAC (International Union of Pure and Applied Chemistry) interlaboratory study of an enzyme-linked immunosorbent screening assay (ELISA) for aflatoxins was conducted in laboratories in Canada, France, Japan, South Africa, Switzerland, The Netherlands, Tunisia, and the United States. Twenty-eight samples of raw and roasted peanuts, corn, whole cottonseed, cottonseed meal, ammoniated cottonseed meal, and poultry feed containing various quantities of natural aflatoxins and supplemented when appropriate with aflatoxin B1 were distributed to participating laboratories for testing. The assay is based on conjugation of pure aflatoxin B1 to an enzyme and the competition between this conjugate and (free) aflatoxins in the product for aflatoxin-specific antibodies coated onto microtiter well walls. After a wash step to remove all unbound aflatoxins, a substrate, added to each well, is catalyzed from a colorless to a green solution by any bound enzyme-conjugated aflatoxin B1 present. The intensity of the color decreases as the amount of free aflatoxin B1 in the product increases. Overall correlation was good between ELISA and thin-layer chromatographic (TLC) results for cottonseed products and mixed feed. Variable results were reported for corn and peanut product samples. Although some positive samples (greater than 15 ng/g) of cottonseed products and mixed feed were reported to contain less than 15 ng/g by visual determination, a review of data for absorbance measurements showed that the contamination level was close to the greater than or equal to 15 ng/g standard and would not have been reported as negative under routine screening.(ABSTRACT TRUNCATED AT 250 WORDS)

Production of Sensitive Monoclonal Antibodies to Aflatoxin B1and Aflatoxin M1 and Their Application to ELISA of Naturally Contaminated Foods.

Two new hybridoma Cell lines capable of secreting sensitive monoclonal antibodies for aflatoxin B1 (AFB1) and aflatoxin M1 (AFM1), were produced by fusing NS-1 myeloma cells with spleen cells of BALB/c female mice immunized with AFB1- and AFM1-carboxymethyloxime bovine serum albumin conjugates, respectively. Detection limits for these antibodies in the direct enzyme-linked immunosorbent assay (ELISA) were 0.5 ng/ml for AFB1 and 0.25 ng/ml for AFM1 Concentrations of AFB1 analogs (ng/ml) required to inhibit 50% binding of AFB1,-perioxidase conjugate to AFB1 monoclonal antibody solid phase in direct ELISA were: AFB1, 2.6; AFB2, 13; AFG1, 8; AFB2, 15; AFM1, 23. Analog concentrations (ng/ml) required to inhibit 50% binding of AFB1,-perioxidase conjugate to AFM1 monoclonal antibody solid phase were: AFM1,0.8; AFM2, 700; AFB1, 0.5; AFB2, 35; AFB2a, >10,000; AFG1, 12; AFG2a, 12; AFP1, 16; and AFQ1, 9.2. These new monoclonal antibodies were applicable to both the ELISA detection AFB1 in corn, cottonseed, cottonseed meal, and mixed feed following a simple extraction in 55% methanol as well as the direct detection of AFM1 in milk.

Enzyme-linked immunosorbent assay of aflatoxin B1 in naturally contaminated corn and cottonseed.

Naturally contaminated corn and cottonseed samples were screened for aflatoxin B1 (AFB1) by a direct competitive enzyme-linked immunosorbent assay (ELISA). Samples were blended 5 min in an extraction solvent of methanol-water-dimethylformamide (70 + 29 + 1) and filtered. Filtrates were assayed by direct competition between AFB1 in the corn and cottonseed samples and AFB1-peroxidase conjugate for binding to specific antibody adsorbed to a solid phase microtiter plate. Standard curves prepared using the extract of AFB1-free corn and cottonseed samples, and extraction solvent only, showed negligible interference by the sample extract in the performance of ELISA. The AFB1 content in corn and dehulled cottonseed samples as determined by ELISA ranged from 7 to 422 micrograms/kg and 7 to 3,258 micrograms/kg, respectively. When ELISA estimates of AFB1 in corn were compared with values obtained by thin layer chromatography (CB method), the correlation coefficient (n = 10) was 0.95. Average interassay and subsample coefficients of variation for ELISA in corn were 21.4 and 22.0%, respectively. When ELISA estimates of AFB1 in cottonseed were compared with values obtained by liquid chromatography (Pons method), the correlation coefficient (n = 15) was 0.96. Using this ELISA, 36 duplicate sample extracts can be screened for AFB1 in less than 2 h.

Hapten-protein conjugates prepared by the mixed anhydride method. Cross-reactive antibodies in heterologous antisera.

Poly-L-lysine conjugates of three structurally unrelated mycotoxins were made by either a mixed anhydride intermediate (MA) or an activated N-hydroxysuccinimide ester intermediate (AE). Control conjugates, with no mycotoxin, were also prepared by each method. Antisera elicited by mycotoxin-albumin conjugates produced by the MA method bound to the three poly-L-lysine-MA mycotoxin conjugates and the MA control conjugate , but bound only to the poly-L-lysine-AE conjugates of the homologous mycotoxin. Binding of antisera to homologous poly-L-lysine conjugates was always inhibited by free hapten when the conjugate was prepared by the AE method but not by the MA method. The specific inhibition of antibody binding by various synthetic haptens indicated that the cross-reactions associated with the MA method were due to the undesired conjugation of isobutylformate during the mixed anhydride procedure.

Indirect enzyme-linked immunosorbent assay for the mycotoxin zearalenone.

A competitive indirect enzyme-linked immunosorbent assay (ELISA) was developed for the detection of zearalenone, an estrogenic mycotoxin. Zearalenone was converted to zearalenone-6'-carboxymethyloxime and conjugated to bovine serum albumin and poly-L-lysine for use as immunogen and solid-phase marker, respectively. Immunization of rabbits with the bovine serum albumin conjugate resulted in zearalenone antibody titers of 20,480 in 11 weeks. A competitive indirect ELISA was conducted by simultaneously incubating zearalenone with zearalenone antiserum over zearalenone-6'-carboxymethyloxime poly-L-lysine solid phase and then determining the bound rabbit immunoglobulin with goat anti-rabbit peroxidase conjugate. Response range for zearalenone in the resulting competition curve was between 1 and 50 ng/ml. Reactivities of this antiserum for alpha-zearalenol, beta-zearalenol, alpha-zearalanol, and beta-zearalanol were, respectively, 50, 12, 6, and 3% of that found for zearalenone. By using the competitive indirect ELISA, zearalenone was detectable in methanol-water extracts of corn, wheat, and pig feed samples.

Deoxynivalenol and 15-monoacetyl deoxynivalenol production by Fusarium graminearum R6576 in liquid media.

Growth and toxigenesis by Fusarium graminearum R6576, were compared in four liquid media. Parameters monitored during the fermentation were deoxynivalenol (DON) and 15-acetyl deoxynivalenol (15-ADON) production, fungal mass, carbohydrate utilization, and pH. Factors which were varied included basal medium composition, corn steep liquor (CSL) concentration, sucrose concentration and ammonium tartrate concentration. Growth in modified Fries medium resulted in only low levels of DON (0.25 mg/L) and 15-ADON (0.25 mg/L) after 20 days. Addition of 4% CSL to modified Fries medium raised the 20 day DON yield to 16.5 mg/l. Increasing the sucrose concentration in modified Fries medium amended with 4% CSL resulted in increased mycelial dry weight but decreased levels of DON. Concentrations of ammonium tartrate greater than 1% in modified Fries amended with 4% CSL greatly reduced DON yield. Use of glucose-yeast extract-peptone (GYEP) for toxin production resulted in higher yields of 15-ADON (14.0 mg/L) than DON (5.5 mg/L) after 20 days. However, supplementation of GYEP with 4% CSL resulted primarily in DON production (4.5 mg/L) after 20 days. In general, qualitative and quantitative production of DON and 15-ADON by Fusarium graminearum R6576 were dependent on the composition of the complex liquid medium.

Detection of T-2 toxin in Fusarium sporotrichioides-infected corn by enzyme-linked immunosorbent assay.

A competitive enzyme-linked immunosorbent assay was used to screen for T-2 toxin in Fusarium sporotrichioides -infected corn. The assay detected T-2 toxin in diluted methanol extracts of corn samples at concentrations of 0.05 ng/ml. In infected corn samples, enzyme-linked immunosorbent assay and gas-liquid chromatography estimations of T-2 toxin concentrations were similar.