Comparative Toxigenicity and Associated Mutagenicity of Aspergillus fumigatus and Aspergillus flavus Group Isolates Collected from the Agricultural Environment

The mutagenic patterns of A. flavus, A. parasiticus and A. fumigatus extracts were evaluated. These strains of toxigenic Aspergillus were collected from the agricultural environment. The Ames test was performed on Salmonella typhimurium strains TA98, TA100 and TA102, without and with S9mix (exogenous metabolic activation system). These data were compared with the mutagenicity of the corresponding pure mycotoxins tested alone or in reconstituted mixtures with equivalent concentrations, in order to investigate the potential interactions between these molecules and/or other natural metabolites. At least 3 mechanisms are involved in the mutagenic response of these aflatoxins: firstly, the formation of AFB1-8,9-epoxide upon addition of S9mix, secondly the likely formation of oxidative damage as indicated by significant responses in TA102, and thirdly, a direct mutagenicity observed for higher doses of some extracts or associated mycotoxins, which does not therefore involve exogenously activated intermediates. Besides the identified mycotoxins (AFB1, AFB2 and AFM1), additional “natural” compounds contribute to the global mutagenicity of the extracts. On the other hand, AFB2 and AFM1 modulate negatively the mutagenicity of AFB1 when mixed in binary or tertiary mixtures. Thus, the evaluation of the mutagenicity of “natural” mixtures is an integrated parameter that better reflects the potential impact of exposure to toxigenic Aspergilli.

Statistical treatment of cytotoxicity in Ames bacterial reverse mutation assays can provide additional structure–activity relationship information

The bacterial reverse mutation assay, that is, the Ames test, measures mutations that reverse the inactivation of a gene involved in the synthesis of either histidine in Salmonella bacteria or tryptophan in Escherichia coli. The classic dose–response curve of an Ames assay plots number of reverse mutations (“revertants”) on the y-axis versus dose of the test chemical on the x-axis. Frequently, the dose–response curve resembles a parabola with a linear initial slope resulting from the accumulation of mutations, which transitions to a downward curvature resulting from cell killing (cytotoxicity) at increasingly higher doses of the test chemical. For regulatory purposes, a positive Ames test is usually considered as induction of twice the number of reverse mutations above background levels. For research purposes, the potency of the mutagenic response can be calculated from measuring the initial slope of the mutagenic response. This initial slope can be calculated in a manner that disentangles the downward pull on the initial slope value provided by the initiation of cytotoxicity. For a dose–response curve resembling a parabola, both the initial positive slope representing mutagenicity and the secondary negative slope representing cytotoxicity can be calculated from the same dose–response curve. The Ames test is the most commonly conducted genotoxicity assay. When a series of molecular congeners are assayed in the Ames test for mutagenicity, additional consideration of the cytotoxicity can provide important structure–activity relationship information.

Induction of Herbicide resistance via seed-derived rice (Oryza sativa) Calli

<div><p><em>Herbicide resistant (HR) rice improves efficiency of weed management and HR varieties can develop through induced mutagenesis. The present investigation was focused on mutagenic response of seed-derived rice calli to different EMS concentrations and evaluation for HR. Seed-derived calli were obtained from glyphosate-susceptible rice variety (Bg250) and exposed to varying concentrations of EMS (0.1%, 0.2%, 0.3% and 0.4%). EMS treated calli were exposed to glyphosate (0.2%) and Tetrazolium test (1% TTC) was applied to identify cell viability in calli. Fluorescent AFLP analysis was performed on EMS treated calli. Results indicated that mutation of calli was higher at EMS concentration range of 0.1 – 0.2%. Bg250 calli demonstrated resistance to glyphosate at 0.2%. FAFLP analysis revealed E11M32 marker was found to be a specific marker to identify the induced HR in rice. The results of the study revealed that in vitro application of EMS on callus has ability to develop HR rice calli. </em></p></div>

Evaluation of Genotoxic Effects of New Molecules with Possible Trypanocidal Activity for Chagas Disease Treatment

Chagas disease is responsible for a large number of human infections and many are also at risk of infection. There is no effective drug for Chagas disease treatment. The Institute of Pharmaceutical Technology at Fiocruz, Brazil, has designed three nitro analogs of the nitroimidazole-thiadiazole, megazol: two triazole analogs PTAL 05-02 and PAMT 09 and a pyrazole analog PTAL 04-09. A set ofSalmonella entericaserovar Typhimurium strains were used in the bacterial reverse mutation test (Ames test) to determine the mutagenicity and cytotoxicity of megazol and its nitro analogs. Megazol presented positive mutagenic activity at very low concentration, either with or without metabolic activation S9 mix. The mutagenic response of the analogs was detected at higher concentration than the lowest megazol concentration to yield mutagenic activity showing that new advances can be made to develop new analogs. The micronucleus test with rat macrophage cells was used in the genotoxic evaluation. The analogs were capable of inducing micronucleus formation and showed cytotoxic effects. PTAL 04-09 structural modifications might be better suitable for the design of promising new drugs candidate for Chagas’ disease treatment.

Comparison of BTX Profiles and Their Mutagenicity Assessment at Two Sites of Agra, India

In the present study, the concentrations of three volatile organic compounds (VOCs), namely, acronym for benzene, toluene, and xylenes (BTX) were assessed because of their role in the tropospheric chemistry. Two representative sites, a roadside and a petrol pump, were chosen for sample collection. VOCs were collected using SKC-activated charcoal tubes and SKC personal sampler and characterized by gas chromatograph using flame ionization detector. Among BTX, benzene had the highest concentration. At the roadside, mean concentration of benzene, toluene, o-,m-xylene, and p-xylene were 14.7 ± 2.4 μgm−3, 8.1 ± 1.2 μgm−3, 2.1 ± 0.8 μgm−3, and 5.1 ± 1.2 μgm−3, respectively. At the petrol pump, the mean concentrations of benzene, toluene, o-,m-xylene and p-xylene were 19.5 ± 3.7 μgm−3, 12.9 ± 1.1 μgm−3, 3.6 ± 0.5 μgm−3and 11.1 ± 1.5 μgm−3, respectively, and were numerically higher by a fraction of 2. Monthly variation of BTX showed maximum concentration in winter. Inter-species ratios and inter-species correlation indicated traffic as the major source of BTX. Extracts of samples were positive in both Salmonella typhimurium tester strains TA98 and TA100 without metabolic activation suggesting the presence of direct mutagens in ambient air that can cause both frame-shift and base-pair mutation. The mutagenic response was greater for TA100 than TA98 suggesting greater activity for base-pair mutagenicity than frame-shift mutagenicity and was found to be statistically significant.

Transcription-Associated Mutation in Bacillus subtilis Cells under Stress

ABSTRACT Adaptive (stationary phase) mutagenesis is a phenomenon by which nondividing cells acquire beneficial mutations as a response to stress. Although the generation of adaptive mutations is essentially stochastic, genetic factors are involved in this phenomenon. We examined how defects in a transcriptional factor, previously reported to alter the acquisition of adaptive mutations, affected mutation levels in a gene under selection. The acquisition of mutations was directly correlated to the level of transcription of a defective leuC allele placed under selection. To further examine the correlation between transcription and adaptive mutation, we placed a point-mutated allele, leuC427, under the control of an inducible promoter and assayed the level of reversion to leucine prototrophy under conditions of leucine starvation. Our results demonstrate that the level of Leu+ reversions increased significantly in parallel with the induced increase in transcription levels. This mutagenic response was not observed under conditions of exponential growth. Since transcription is a ubiquitous biological process, transcription-associated mutagenesis may influence evolutionary processes in all organisms.