Cell Cycle Characteristics of Crenarchaeota : Unity among Diversity

The hyperthermophilic archaeaAcidianus hospitalis ,Aeropyrum pernix ,Pyrobaculum aerophilum ,Pyrobaculum calidifontis , andSulfolobus tokodaii representing three different orders in the phylumCrenarchaeota were analyzed by flow cytometry and combined phase-contrast and epifluorescence microscopy. The overall organization of the cell cycle was found to be similar in all species, with a short prereplicative period and a dominant postreplicative period that accounted for 64 to 77% of the generation time. Thus, in allCrenarchaeota analyzed to date, cell division and initiation of chromosome replication occur in close succession, and a long time interval separates termination of replication from cell division. InPyrobaculum , chromosome segregation overlapped with or closely followed DNA replication, and further genome separation appeared to occur concomitant with cellular growth. Cell division inP. aerophilum took place without visible constriction.