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Chromosome age and segregation during sporulation of Bacillus megaterium
Abstract:
The effect of chromosome age on segregation during sporulation was investigated. Vegetative cells of Bacillus megaterium were labeled with [Me-3H]thymine and then were grown at 30 degrees C in nonradioactive medium for various times before being allowed to sporulate. The ratio of the amount of label in sporal DNA to that in sporangial DNA, obtained after minor correction for the sporulation frequency, remained essentially constant as the postlabeling growth period was increased from one to seven generations. The spores were preferentially located at the older poles of sporangia, i.e. the poles formed by divisions occurring prior to those forming the sporangia. Therefore, it seems that old (labeled) chromosomes segregate randomly with respect to both the morphological and genealogical polarities of sporangia. Examination of total cell lysates by dye-buoyant density gradient centrifugation revealed the presence of covalently closed circular DNA from cells grown at 37 degrees C, but none was obtained from cells grown at 30 degrees C. Thus, possible interference by large amounts of extrachromosomal DNA in the determination of the chromosomal segregation pattern is unlikely.
Insights
Investigating chromosome age in Bacillus megaterium sporulation revealed that older chromosomes segregate randomly. This finding clarifies chromosomal behavior during bacterial cell division and spore formation.
Area of Science:
- Microbiology
- Cell Biology
- Genetics
Background:
- Bacterial sporulation is a complex process involving cell division and differentiation.
- Understanding chromosome segregation is crucial for bacterial genetics and reproduction.
- The role of chromosome age in segregation patterns during sporulation was previously unclear.
Purpose of the Study:
- To investigate the effect of chromosome age on DNA segregation during Bacillus megaterium sporulation.
- To determine if older chromosomes exhibit preferential segregation patterns.
Main Methods:
- Vegetative Bacillus megaterium cells were labeled with [Me-3H]thymine.
- Cells were grown for varying periods (1-7 generations) in nonradioactive medium before sporulation.
- Radioactivity in sporal DNA versus sporangial DNA was quantified.
- Dye-buoyant density gradient centrifugation was used to assess extrachromosomal DNA.
Main Results:
- The ratio of labeled DNA in spores to sporangia remained constant across different postlabeling growth periods.
- Spores were preferentially located at older poles of sporangia.
- No significant interference from extrachromosomal DNA was detected at 30°C.
Conclusions:
- Old chromosomes in Bacillus megaterium segregate randomly with respect to both morphological and genealogical polarities.
- Extrachromosomal DNA does not appear to interfere with the observed chromosomal segregation patterns under the tested conditions.