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Journal of Bacteriology, October 1999, p. 6073-6080, Vol. 181, No. 19
Department of Biology, Graduate School of Science, Osaka
City University, Sumiyoshi-ku, Osaka 558-8585, Japan
Received 8 January 1999/Accepted 17 May 1999
The nucleoids in Mycoplasma capricolum cells were
visualized by phase-combined fluorescence microscopy of DAPI
(4',6-diamidino-2-phenylindole)-stained cells. Most growing cells in a
rich medium had one or two nucleoids in a cell, and no anucleate cells
were found. The nucleoids were positioned in the center in mononucleoid
cells and at one-quarter and three-quarters of the cell length in
binucleoid cells. These formations may have the purpose of ensuring
delivery of replicated DNA to daughter cells. Internucleoid distances
in binucleoid cells correlated with the cell lengths, and the
relationship of DNA content to cell length showed that cell length
depended on DNA content in binucleoid cells but not in mononucleoid
cells. These observations suggest that cell elongation takes place in
combination with nucleoid movement. Lipid synthesis was inhibited by
transfer of cells to a medium lacking supplementation for lipid
synthesis. The transferred cells immediately stopped dividing and
elongated while regular spaces were maintained between the nucleoids
for 1 h. After 1 h, the cells changed their shapes from
rod-like to round, but the proportion of multinucleoid cells increased.
Inhibition of protein synthesis by chloramphenicol induced nucleoid
condensation and abnormal positioning, although partitioning was not
inhibited. These results suggest that nucleoid partitioning does not
require lipid or protein synthesis, while regular positioning requires both. When DNA replication was inhibited, the cells formed branches, and the nucleoids were positioned at the branching points. A model for
the reproduction process of M. capricolum, including
nucleoid migration and cell division, is discussed.
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Partitioning, Movement, and Positioning of
Nucleoids in Mycoplasma capricolum
*
Corresponding author. Mailing address: Department of
Biology, Graduate School of Science, Osaka City University,
Sumiyoshi-ku, Osaka 558-8585, Japan. Phone: 81(6)6605 3157. Fax:
81(6)6605 2522. E-mail: miyata{at}sci.osaka-cu.ac.jp.
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