Chromosomal Replication, Plasmid Replication, and Cell Division

Abstract

The study of chromosomal replication and cell division of bacteria has extended beyond Escherichia coli, and important insights have emerged recently from studies in other species, especially Bacillus subtilis and Caulobacter crescentus. Cell division is coordinated with other cell cycle events such as genomic DNA synthesis that leads to chromosomal replication and partition, increase of cell mass, and cell expansion by cell wall synthesis. This chapter reviews the information about predicted genes related to chromosomal replication, plasmid replication, and cell division in Helicobacter pylori, and a plausible replication machinery of the bacterium is discussed in light of the current understanding of bacterial organization and function of replication and cell division. The DnaA protein is essential for the initiation of chromosomal replication and is highly conserved among different bacteria. Clinical isolates of H. pylori have been reported to carry plasmids ranging in size from 1.5 to 40 kb. Three cryptic plasmids, pHPK225 (1.5 kb), pHPM180 (3.5 kb), and pHell (2.9 kb), have been completely sequenced. Cell division of gram-negative bacteria proceeds through nucleoid segregation, partitioning of the cytoplasm into two compartments each containing a copy of the cell's genetic information, and invagination of the three layers of the cell envelope between the chromosome. Chromosomal replication and cell division of bacteria are well-organized and coordinately regulated processes operated by a complex genetic machinery. H. pylori seems to possess almost all the components known to be involved in chromosomal replication and cell division in E. coli.