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A mutant strain of Polysphondylium with defects in many genes
Abstract:
PN6024 is a mutant strain of P. pallidum which appeared on selection for resistance to MDMP, an inhibitor of translation. It was found to be mutant in four other traits, being resistant to tubercidin, incapable of growth at 31.5 degrees C, abnormal in development, and slow growing at 25 degrees C. Genetic crosses using the macrocyst cycle showed that these five traits are controlled by five unlinked genes. The hypothesis is that movement of a transposon to multiple new locations caused these mutations. A difference in restriction fragment pattern between PN6024 and its parent PN600 support the hypothesis. Attempts were made to find conditions generating other strains like PN6024. Selection for growth in the presence of tubercidin yielded clones which resemble PN6024 in being developmentally abnormal as well as tubercidin resistant. Tubercidin treatment also increased the frequency of clones resistant to canavanine. It is suggested that tubercidin is mutagenic because it causes movement of the putative transposon, not because it generates point mutations. Growth under conditions of stress (at 31.5 degrees C, at 8 degrees C, in the presence of 2% ethanol) had at most an erratic effect in generating strains like PN6024. Three substrains appeared spontaneously in cultures of PN6024. These differed in developmental characteristics from each other and from the parent strain. It is suggested that they carry mutations in genes which control the choices between growth and aggregation, and between aggregation and encystment.
Insights
A novel mutant strain of *P. pallidum*, PN6024, exhibits resistance to translation inhibitors and displays altered growth and development. These mutations are linked to transposon activity, suggesting a mechanism for genetic variation in this organism.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- *P. pallidum* is a parasitic bacterium with a complex life cycle.
- Understanding genetic variation and mutation mechanisms is crucial for studying parasitic organisms.
Purpose of the Study:
- To investigate the genetic basis of a novel mutant strain, PN6024, of *P. pallidum*.
- To explore the role of transposon activity in generating multiple mutations and phenotypic changes.
Main Methods:
- Phenotypic characterization of the PN6024 mutant strain.
- Genetic crosses using the *P. pallidum* macrocyst cycle.
- Restriction fragment analysis to compare mutant and parent strains.
- Selection experiments under various stress conditions (e.g., drug resistance, temperature).
Main Results:
- PN6024 displayed resistance to MDMP and tubercidin, impaired growth at elevated temperatures, abnormal development, and slow growth.
- Five unlinked genes controlled these distinct traits, supporting a multi-site mutation hypothesis.
- Restriction fragment pattern differences indicated transposon movement.
- Tubercidin exposure induced similar developmental abnormalities and canavanine resistance, suggesting a mutagenic role via transposon activation.
Conclusions:
- Transposon mobilization is a likely mechanism driving the multiple mutations observed in PN6024.
- Tubercidin acts as a mutagen by inducing transposon movement rather than direct point mutations.
- Spontaneous substrains of PN6024 suggest mutations affecting developmental pathway choices.