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Mutagenic DNA repair in Streptomyces
Abstract:
Streptomyces fradiae JS6 (mcr-6) is defective in the repair of potentially lethal damage to DNA induced by mitomycin C (MC), hydroxylamine (NH2OH), methyl methanesulfonate (MMS), 4-nitroquinoline 1-oxide (NQO), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and ultraviolet light (UV), but it exhibits nearly normal sensitivity to ethyl methanesulfonate (EMS)-induced lethality. JS6 is substantially less mutable by MNNG, MMS, NQO, UV, NH2OH, and also EMS than is the parental strain. A spontaneous revertant of JS6 showed wild-type levels of resistance to all of these agents and wild-type levels of induced mutagenesis, indicating that a single mutation caused the multiple traits displayed by JS6. The mcr-6 gene product thus appears to control an error-prone (mutagenic) DNA repair system. Mediation of EMS mutagenesis by an error-prone repair pathway in S. fradiae, rather than by direct mispairing as in Escherichia coli, suggests that the streptomycetes have evolved more efficient error-avoidance mechanisms than those commonly observed in the single-celled eubacteria.
Insights
Streptomyces fradiae JS6 exhibits defective DNA repair and reduced mutation rates after exposure to various damaging agents. A single mutation in the mcr-6 gene controls this error-prone DNA repair system.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- DNA repair mechanisms are crucial for maintaining genomic stability.
- Streptomyces species are important antibiotic producers with complex genomes.
- Understanding DNA repair pathways can reveal insights into microbial evolution and drug resistance.
Purpose of the Study:
- To investigate the DNA repair defect in Streptomyces fradiae JS6 (mcr-6).
- To identify the genetic basis for altered sensitivity and mutability to DNA-damaging agents.
- To elucidate the role of the mcr-6 gene product in DNA repair and mutagenesis.
Main Methods:
- Phenotypic characterization of Streptomyces fradiae JS6 and its revertant.
- Assessing sensitivity to DNA-damaging agents: mitomycin C, hydroxylamine, methyl methanesulfonate, 4-nitroquinoline 1-oxide, N-methyl-N'-nitro-N-nitrosoguanidine, and ultraviolet light.
- Evaluating mutagenesis rates induced by these agents.
Main Results:
- Streptomyces fradiae JS6 (mcr-6) showed defective repair of DNA damage induced by MC, NH2OH, MMS, NQO, MNNG, and UV.
- JS6 exhibited significantly reduced mutability by these agents compared to the parental strain.
- A spontaneous revertant displayed wild-type resistance and mutagenesis levels, indicating a single gene mutation (mcr-6).
Conclusions:
- The mcr-6 gene product regulates an error-prone DNA repair system in Streptomyces fradiae.
- This system mediates mutagenesis, distinct from direct mispairing observed in Escherichia coli.
- Streptomycetes may possess evolved error-avoidance mechanisms superior to those in simpler bacteria.