On the cell cycle of Escherichia coli and cell division in Haloferax mediterranei

Sammanfattning: Escherichia coli has served as a model organism for prokaryotes for several decades and is perhaps the most well characterised organism on earth. The use of fluorescence microscopy during recent years has contributed substantially to our understanding of the essential cell cycle processes chromosome replication, chromosome segregation and cell division.In this thesis, the co-ordination between chromosome replication and cell division has been investigated. It was found that cell division does not have to take place within a certain time after chromosome replication and that in the absence of chromosome replication, cell division is initiated but is most often not completed. Furthermore, the condensation state of non-replicating chromosomes was demonstrated to be severely affected in vivo in the absence of the protein MukB. Chromosome segregation disturbances were quantified in cells with a defective Min system, which is normally involved in directing cell division to the center of the cell. Possible causes for this disturbed chromosome segregation were investigated. Some E. coli strains form branched cells with a high frequency and the mechanism for the formation of branches was investigated. Branches were formed also after inhibition of cell division, showing that the cell division machinery is not required for the emergence of branches.Prokaryotes are divided into two main, evolutionary defined groups; Archaea and Bacteria, the last common ancestor of which might have lived 3-4 billion years ago. Here, cell division in the archaeon Haloferax mediterranei was demonstrated to share features with cell division in other archaea and bacteria, including E. coli.