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Cholorate toxicity in Aspergillus nidulans: the selection and characterisation of chlorate resistant mutants
Abstract:
Mutation in at least ten genes can result in chlorate reistance in Aspergillus nidulans. Mutation in seven of these genes also results in the inability to use nitrate as nitrogen source. The various classes of resistant mutant obtained occur in different proportions, depending on whether or not a mutagenic treatment is employed, and also on which nitrogen source is used for selection. The prinicipal effect of mutagen arises because mutations in the niaD gene, the nitrate reductase structural gene, are relatively much commoner when no mutagen is used than after treatment with N-methyl-N'-nitro-N-nitrosoguanidine. This may be connected with the finding that deletions involving the niaD gene are relatively more common among samples of spontaneous niaD mutants. Some of these deletions extend to the neighbouring niiA gene, the structural gene for nitrite reductase. The selection procedures used were designed to avoid bias in favour of any particular chlorate resistant phenotype. Even if biases existed however, these could not account for the variation found from nitrogren source to nitrogen source in the proportions of certain resistant classes having apparently identical chlorate resistance phenotypes.
Insights
Chlorate resistance in Aspergillus nidulans involves mutations in multiple genes. Mutagenesis affects the frequency of specific mutations, particularly in nitrate reductase genes, influencing nitrogen utilization.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Chlorate resistance in Aspergillus nidulans is a complex trait.
- Mutations in at least ten genes can confer chlorate resistance.
- Seven of these genes are also essential for utilizing nitrate as a nitrogen source.
Purpose of the Study:
- To investigate the genetic basis of chlorate resistance in Aspergillus nidulans.
- To understand the influence of mutagens and nitrogen sources on the selection of resistant mutants.
- To analyze the frequency and nature of mutations in key genes like niaD and niiA.
Main Methods:
- Selection of chlorate-resistant mutants under different conditions (with and without mutagens, various nitrogen sources).
- Analysis of mutation types, including deletions, in specific genes (niaD, niiA).
- Phenotypic characterization of resistant mutants.
Main Results:
- The proportion of different chlorate-resistant mutant classes varies significantly based on mutagenic treatment and nitrogen source.
- Mutations in the niaD gene (nitrate reductase) are more frequent in spontaneous mutants than after N-methyl-N'-nitro-N-nitrosoguanidine treatment.
- Deletions involving niaD, and sometimes the adjacent niiA gene (nitrite reductase), are common among spontaneous niaD mutants.
Conclusions:
- The frequency of specific mutations conferring chlorate resistance is influenced by mutagenic agents.
- Spontaneous mutations, particularly deletions, play a significant role in niaD and niiA gene alterations.
- Observed variations in mutant proportions cannot be solely explained by selection biases, suggesting complex genetic interactions.
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