Nucleoid structure and partition in Methanococcus jannaschii: an archaeon with multiple copies of the chromosome.

We measured different cellular parameters in the methanogenic archaeon Methanococcus jannaschii. In exponential growth phase, the cells contained multiple chromosomes and displayed a broad variation in size and DNA content. In most cells, the nucleoids were organized into a thread-like network, although less complex structures also were observed. During entry into stationary phase, chromosome replication continued to termination while no new rounds were initiated: the cells ended up with one to five chromosomes per cell with no apparent preference for any given DNA content. Most cells in stationary phase contained more than one genome equivalent. Asymmetric divisions were detected in stationary phase, and the nucleoids were found to be significantly more compact than in exponential phase.