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Journal of Bacteriology, September 1999, p. 5669-5675, Vol. 181, No. 18
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Changes in Cell Size and DNA Content in Sulfolobus Cultures during Dilution and Temperature Shift Experiments

Karin Hjort and Rolf Bernander*

Department of Cell and Molecular Biology, Biomedical Center, Uppsala University, SE-751 24 Uppsala, Sweden

Received 30 April 1999/Accepted 7 July 1999

Stationary-phase cultures of different hyperthermophilic species of the archaeal genus Sulfolobus were diluted into fresh growth medium and analyzed by flow cytometry and phase-fluorescence microscopy. After dilution, cellular growth started rapidly but no nucleoid partition, cell division, or chromosome replication took place until the cells had been increasing in size for several hours. Initiation of chromosome replication required that the cells first go through partition and cell division, revealing a strong interdependence between these key cell cycle events. The time points at which nucleoid partition, division, and replication occurred after the dilution were used to estimate the relative lengths of the cell cycle periods. When exponentially growing cultures were diluted into fresh growth medium, there was an unexpected transient inhibition of growth and cell division, showing that the cultures did not maintain balanced growth. Furthermore, when cultures growing at 79°C were shifted to room temperature or to ice-water baths, the cells were found to "freeze" in mid-growth. After a shift back to 79°C, growth, replication, and division rapidly resumed and the mode and kinetics of the resumption differed depending upon the nature and length of the shifts. Dilution of stationary-phase cultures provides a simple protocol for the generation of partially synchronized populations that may be used to study cell cycle-specific events.

* Corresponding author. Mailing address: Department of Cell and Molecular Biology, Box 596, Biomedical Center, Uppsala University, SE-751 24 Uppsala, Sweden. Phone: 46 18 471 4058. Fax: 46 18 53 03 96. E-mail: Rolf.Bernander{at}icm.uu.se.

Journal of Bacteriology, September 1999, p. 5669-5675, Vol. 181, No. 18
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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