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Most bacteria contain one circular chromosome; the chromosomal
replication is initiated at a single origin, oriC, elongated bi-directionally and terminated at the antipode, ter. The cell cycle is divided into three periods: B(irth), C(hromosomal replication), and D(ivision). The Cooper-Helmstetter model describes the relationship between chromosomal replication and the parameters: C, D and the doubling-time. The relation between cell age and DNA-content is given by this model.
Flow cytometry enable the determination of the size and DNA content for a large number of cells. Often, replication initiation and cell division is arrested with drugs before cells are subjected to flow cytometry to obtain information on origin to cell ratio and the synchrony of initiation. The use of drugs may introduce artifacts on DNA replication. Therefor drug-free methods are preferred to infer the cell cycle parameters.
Simulation of DNA distributions in exponentially growing cells has
originally been used to estimate the B, C, and D for single-chromosome cells in Escherihia coli by others. In recent years cell cycle studies have been applied to bacteria deviating from the "single origin single circular chromosome" paradigm such as Vibrio cholera (two circular chromosomes) and Sulfolobus sp. and engineered E. coli (multiple origins on one chromosome). We have earlier extended the DNA simulation method to estimate cell cycle parameters for wild type and engineered V. cholerae.
Here we present and discuss our recent developments in cell cycle simulation including simulation of both cell mass and DNA distribution in 3D.