Structure and Function of the Bacterial Genome. Charles J. Dorman

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Structure and Function of the Bacterial Genome - Charles J. Dorman


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and was cultured in Palo Alto, California, USA, in 1922 (Bachmann 1996). This isolate was the ancestor of W1485 from the Joshua Lederberg laboratory, the isolate that was named MG1655 by Mark Guyer (hence ‘MG’). The first E. coli chromosome to be sequenced came from this intensively studied MG1655 strain (Blattner et al. 1997). However, this was not the first bacterial chromosome to have its complete nucleotide sequence determined: that honour belongs to Haemophilus influenza (Fleischmann et al. 1995).

      The E. coli K‐12 chromosome is a single, covalently closed, circular, double‐stranded DNA molecule of 4 639 221 bp (Blattner et al. 1997). Although chromosome circularity is the norm in E. coli, cells in which the chromosome is artificially linearised (with the ends closed by hairpin turns) are viable, show few alterations in gene expression, have normal nucleoid structure, and do not display growth defects (Cui et al. 2007). Thus, the circular nature of the chromosome is not essential for its functionality or for its ability to be replicated and to be segregated at cell division.

      Most of our knowledge about chromosome replication and segregation comes from studying a handful of model organisms: E. coli, Caulobacter crescentus, Vibrio cholerae, and Bacillus subtilis. The focus in this chapter will be on E. coli, with comparisons to other organisms where this is useful.

      Chromosome replication, segregation, and cell division are complex processes that must be coordinated to ensure the successful replication of the cell (Reyes‐Lamothe et al. 2012). The nutritional status of the cell and its metabolic flux are very influential in achieving this coordination and they have a direct bearing on the growth rate of the culture (Wang and Levin 2009).

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