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Sequential entry of transforming markers into Neisseria meningitidis after chromosome alignment
Abstract:
The kinetics of appearance of transformants as a function of time of exposure to deoxyribonucleic acid (DNA) was examined in Neisseria meningitidis. Incubation with chloramphenicol for as long as 2 hr, which probably leads to chromosome alignment, resulted in augmentation of the lag period before the appearance of the first transformants. The lag periods thus found were dependent upon the marker tested. This permitted the construction of a time map according to the lag periods observed for individual markers. This map was in general agreement with the chromosome map of the recipient strain as determined by marker frequency analysis. Transformation of recipient cells with chromosomes aligned by growth to the stationary phase showed the same type of increased lag in the appearance of transformants before the logarithmic phase of growth had again been reached. These results support the assumption that the nature of the marker accepted by a recipient cell corresponds to the marker present at the replication point of the chromosome. In the absence of DNA and protein synthesis, the uptake of one marker seems to be successively followed by other markers in a linear order determined by the chromosome of the recipient cell.
Insights
This study in Neisseria meningitidis reveals that deoxyribonucleic acid (DNA) transformation kinetics are influenced by chromosome alignment. Marker-dependent lag periods allowed mapping of the bacterial chromosome.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Bacterial transformation is a key mechanism for genetic exchange.
- Understanding the kinetics of transformation provides insights into DNA uptake and chromosomal integration.
- Neisseria meningitidis is a significant human pathogen where transformation plays a role in genetic diversity.
Purpose of the Study:
- To investigate the kinetics of transformant appearance in Neisseria meningitidis as a function of deoxyribonucleic acid (DNA) exposure time.
- To determine the influence of cellular processes, such as chromosome alignment, on transformation efficiency and lag periods.
- To construct a temporal map of the bacterial chromosome based on transformation kinetics.
Main Methods:
- Examining the kinetics of transformant appearance over time after exposure to DNA.
- Utilizing chloramphenicol treatment to induce chromosome alignment and observing its effect on lag periods.
- Comparing lag periods for different genetic markers to construct a time map.
- Correlating the time map with existing chromosome maps derived from marker frequency analysis.
- Analyzing transformation in cells with aligned chromosomes (stationary phase) and assessing lag periods upon re-initiation of growth.
Main Results:
- Incubation with chloramphenicol, promoting chromosome alignment, extended the lag period before transformant appearance.
- Lag periods were dependent on the specific genetic marker being tested.
- A time map constructed from lag periods showed good agreement with the recipient strain's chromosome map.
- Transformation of stationary phase cells (with aligned chromosomes) exhibited similar increased lag periods.
- These findings support the model where the accepted marker aligns with the chromosome's replication point.
Conclusions:
- Chromosome alignment in Neisseria meningitidis significantly impacts deoxyribonucleic acid (DNA) transformation kinetics, specifically by increasing lag periods.
- The marker-dependent lag periods enable the creation of a temporal map of the bacterial chromosome.
- The results strongly suggest that the integration of incoming DNA is guided by the position of the marker at the chromosome's replication point.
- This study provides a novel method for bacterial chromosome mapping and sheds light on the mechanism of DNA integration during transformation.