Cell cycle analysis of archaea
Abstract: In my thesis, the cell cycle analysis of archaea and hyperthermophilic organisms is presented for the first time. Crenarchaea from the genus Sulfolobus were used as a model system. Plow cytometry and light microscopy were applied to investigate the timing and coordination of different cell cycle events. Furthermore, DNA content, nucleoid structure, and nucleoid distribution at different stages during the cell cycle were studied. The Sulfolobus cell cycle was characterized as having a short pre-replication and a long post-replication period. The presence of a low proportion of cells with segregated genomes in the exponentially growing population suggested 3 considerable time delay between termination of chromosome replication and completion of nucleoid partition, reminiscent of the G2 period in eukaryotic cells.The first available collection of conditional-lethal mutants of any archaeon or hyperthemophile was used to elucidate the coordination of cell cycle events. The studies showed that chromosome replication, nucleoid partition and cell division in Sulfolobus acidocaldarius, which are normally tightly coordinated during cellular growth, could be separately inhibited or uncoupled by mutation.The ftsZ gene, which is involved in cell division in bacteria and euryarchaea, was isolated from the halophilic archaeon Haloferax mediterranei. Transcriptional start sites were mapped, and putative translation initiation elements were identified. In both the upstream and downstream regions of the ftsZ gene, open reading frames were found to be conserved within the genus Haloferax. Furthermore, at the 3' end of the ftsZ gene, the homologs of the bacterial secE and nusG genes are conserved in almost all euryarchaea analyzed so far. The studies also demonstrated the functional conservation of the FtsZ protein in different archaeal species, as well as between euryarchaea and bacteria.
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