The role of extrolites secreted by nonaflatoxigenic Aspergillus flavus in biocontrol efficacy.

AIMS: Field control of aflatoxin contamination is thought to occur through competitive exclusion of native aflatoxigenic fungi by introduced nonaflatoxigenic Aspergillus flavus biocontrol strains. In this study, we explored another possible mechanism that could increase the efficacy of biocontrol strains-the production of secreted compounds termed extrolites. METHODS AND RESULTS: Using four Aspergillus strains (one nonaflatoxigenic and three aflatoxigenic) from the same geographic region (Louisiana), we devised experiments whereby each aflatoxigenic strain was grown on media that had first been colonized by the nonaflatoxigenic strain. We observed noticeable reduction in growth and reduced production of aflatoxin and cyclopiazonic acid for all three aflatoxigenic strains when grown in the presence of extrolite secretions from the nonaflatoxigenic strain. CONCLUSIONS: We provide evidence that biocontrol strain extrolites may improve the efficacy of pre and postharvest aflatoxin reduction. SIGNIFICANCE AND IMPACT OF THE STUDY: Our finding, that extrolites secreted by nonaflatoxigenic A. flavus strains potentially abate growth and toxin levels of aflatoxin-producing strains, should allow for us to elucidate the mechanism of how the reduction in toxigenic strains occurs, and potentially identify better biocontrol strains. Identification and isolation of the active extrolites may afford a supplemental method to mitigate aflatoxin production.

Analysis of genetic and aflatoxin diversity among Aspergillus flavus isolates collected from sorghum seeds.

Thirty-four Aspergillus flavus isolates were recovered from sorghum seeds sampled across five states in India. Our study included (1) species confirmation through PCR assay, (2) quantification of total aflatoxin concentrations by the indirect competitive-ELISA (ic-ELISA) method, and (3) analysis of molecular diversity among the A. flavus isolates using ß-tubulin, ITS, and ISSR markers. Among the isolates studied, 28 were found to be positive for the production of aflatoxins. ITS and ß-tubulin phylogenetic analysis segregated the A. flavus sample population into two major groups or clades with little to no subdivision based on geography. In contrast, ISSR analysis also separated the A. flavus isolates into two main clusters, showing a distance of 0.0-0.5, with one cluster exhibiting a high level of diversity though no geographic or chemotype subdivision could be observed. The majority of sampled A. flavus isolates were highly toxigenic, and also highly diversified in terms of toxin-producing potential in-vitro. Genetic diversity among the sorghum isolates of A. flavus further warrants the development of appropriate farming management practices as well as improved aflatoxin detection measures in India.

Growth inhibitory effects of gossypol and related compounds on fungal cotton root pathogens.

UNLABELLED: The effect of the terpenoids gossypol, 6-methoxygossypol, 6,6'-dimethoxygossypol, gossypolone and apogossypolone on growth of fungal soil pathogens was investigated. The compounds were tested at a concentration of 100 µg ml(-1) in a Czapek Dox agar medium at 25°C. Gossypol, gossypolone and apogossypolone demonstrated strong growth inhibitory activity (≥90%) against Pythium irregulare, Pythium ultimum and Fusarium oxysporum. These same terpenoids provided good growth inhibition against most Rhizoctonia solani isolates. Methylated gossypol derivatives generally yielded reduced growth inhibition against the tested fungi compared with gossypol. Dose-response effects of gossypol, gossypolone and apogossypolone were determined over a concentration range of 5-100 µg ml(-1) against P. irregulare CR1, P. ultimum ATCC 56081 and R. solani CR15. At lower concentrations, gossypol proved to be a more potent growth inhibitor of P. irregulare (ED50  = 4 µg ml(-1) ) and P. ultimum (ED50  = 13·2 µg ml(-1) ) than the other tested compounds. Rhizoctonia solani CR15 was more resistant to growth inhibitory effects of all tested terpenoids (ED50  = 35-43 µg ml(-1) ). SIGNIFICANCE AND IMPACT OF THE STUDY: This work demonstrates that gossypol is an effective natural antimicrobial agent against a wide range of potential fungal pathogens of cotton. Relative to gossypol, methylated gossypol derivatives that are also found naturally in root tissue were less effective at inhibiting the growth of soil fungal pathogens. However, by virtue of their significant concentration in root tissue, they still may contribute to cotton defence.

Comparison of anti-inflammatory compounds in the carrageenan induced paw edema model and the reversed passive Arthus model utilizing the same animal.

In order to better define antiinflammatory activity in new agents, a test was devised utilizing both carrageenan induced paw edema and the reversed passive Arthus reaction in the same animal. The model of carrageenan induced rat paw edema is a standard laboratory assay used to predict classical "aspirin-like" antiinflammatory molecules. The reversed passive cutaneous Arthus reaction involves precipitating antigen-antibody complexes, complement and infiltrating polymorphonuclear leukocytes (PMN's) and can be used to identify agents that affect one or more of these factors specifically. Antiinflammatory compounds were given orally one hour prior to the administration of carrageenan and goat anti-rat serum. Comparisons were made between several non-steroidal compounds and the steroid hydrocortisone. All of the compounds tested gave good carrageenan activity, but only hydrocortisone produced significant Arthus lesion inhibition in this assay.

2,6-Di-tert-butyl-4-(2'-thenoyl)phenol(R-830): a novel nonsteroidal anti-inflammatory agent with antioxidant properties.

R-830, a di-tert-butylphenol, has been shown to be anti-inflammatory in a number of animal models. These include conventional systems such as carrageenan-induced edema and adjuvant arthritis of the rat and ultraviolet-induced erythema in the guinea pig in which the acidic nonsteroidal anti-inflammatory drugs (e.g., indomethacin) are effective. The anti-inflammatory activity of R-830 has also been demonstrated in other models (e.g., graft vs. host reaction and reversed passive cutaneous Arthus reaction in the rat, contact sensitivity in the mouse) in which the acidic nonsteroidal drugs are not effective. In vitro, R-830 inhibits guinea pig lung lipoxygenase and bovine seminal vesicle cyclo-oxygenase. The antioxidant properties of R-830 were demonstrated in two in vitro systems. We speculate that the antioxidant activity of this molecule might be related to its unusual profile of pharmacological activity.

4-nitro-2-phenoxymethanesulfonanilide (R-805): a chemically novel anti-inflammatory agent.

The anti-inflammatory activity of the sulfonanilide, 4-nitro-2-phenoxymethanesulfonanilide (R-805) has been demonstrated in conventional models (carrageenan-induced edema of the rat's paw, UV-induced erythema of guinea-pig skin, adjuvant-induced arthritis of the rat). R-805 differs from most currently available acidic anti-inflammatory drugs in that its functional acidic group is not carboxyl. The relative anti-inflammatory potency of R-805 is comparable to indomethacin. Calculation of acute therapeutic indices (LD50/ED50) for 8 acidic anti-inflammatory drugs show R-805 to possess a more favourable index than the other drugs examined.

Antiinflammatory fluoroalkanesulfonanilides. 3. Other fluoroalkanesulfonamido diaryl systems.

A series of isosteres of 3-benzoyltrifluoromethanesulfonanilide involving alternatives to the carbonyl linking group was synthesized and screened for antiinflammatory activity in the carrageenan rat paw edema test. The systems examined were of the type m-CF3SO2NH-C6H4-X-C6H5, where X was -CROH-, -CHR-, -CH(OH)CH2-, -COCH2-, -CH2CO-, greater than C equal to CR2, -CR equal to CH, -C identical to C-, -CH2CH2-, CONH-, -NR-, -O-, -S(O)n- (n equal to 0,1,2), and carbon-carbon single bond. Many ortho and para derivatives were also tested. Several of these new trifluoromethanesulfonanilides proved equipotent with phenylbutazone. The effects on the anticarrageenan activity of both the nature and ring position of X are discussed.