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Cell wall assembly during inhibition of DNA synthesis in Streptococcus faecium
Abstract:
Growth sites which are bounded by raised wall bands can be observed in electron micrographs of replicas of Streptococcus faecium. When mitomycin C was added to an exponential-phase culture doubling in mass every 64 min, DNA synthesis was inhibited, and eventually cell division stopped. The growth sites formed before and after inhibition of DNA synthesis enlarged until they contained about 0.25 micron3 of cell volume, at which point they ceased to increase in size. When these sites approached this 0.25-micron3 limit, new sites were initiated; this result had also been observed in untreated cells undergoing a large range of exponential-phase mass doubling times. Thus, regardless of whether chromosome replication is inhibited or uninhibited, sites have the same finite capacity to enlarge to about 0.25 micron3, and when this capacity is reached, new sites are initiated. Although initiation of new growth sites seems to be independent of normal chromosome replication, these results confirm previous studies showing that chromosome replication is necessary for the terminal events of growth site development which result in the division of a site into two separate poles. Two classes of models for the regulation of growth site initiation are discussed.
Insights
Bacterial growth sites in Streptococcus faecium have a finite capacity, reaching about 0.25 micron3 before initiating new sites. This initiation is independent of DNA replication but necessary for cell division.
Area of Science:
- Microbiology
- Cell Biology
- Bacterial Growth Regulation
Background:
- Streptococcus faecium exhibits distinct growth sites demarcated by raised wall bands.
- Cell division and DNA synthesis are critical processes in bacterial proliferation.
Purpose of the Study:
- To investigate the regulation of bacterial growth site initiation in Streptococcus faecium.
- To determine the relationship between DNA synthesis inhibition and growth site development.
Main Methods:
- Utilized electron microscopy to visualize growth sites in Streptococcus faecium replicas.
- Inhibited DNA synthesis using mitomycin C in exponentially growing cultures.
- Monitored growth site enlargement and initiation under inhibited and uninhibited conditions.
Main Results:
- Growth sites enlarged to a finite volume of approximately 0.25 micron3 before ceasing to grow.
- New growth sites were initiated when existing sites approached this volume limit, irrespective of DNA synthesis.
- Chromosome replication inhibition did not prevent growth site initiation but was essential for terminal division events.
Conclusions:
- Growth site initiation in Streptococcus faecium is regulated by a finite size capacity, independent of immediate DNA replication.
- While initiation is separable from DNA synthesis, chromosome replication remains crucial for the completion of cell division.
- The findings support models where growth site initiation and terminal division are distinct, yet coordinated, cellular processes.