Intensive DNA Replication and Metabolism during the Lag Phase in Cyanobacteria.
Unlike bacteria such as Escherichia coli and Bacillus subtilis, several species of freshwater cyanobacteria are known to contain multiple chromosomal copies per cell, at all stages of their cell cycle. We have characterized the replication of multi-copy chromosomes in the cyanobacterium Synechococcus elongatus PCC 7942 (hereafter Synechococcus 7942). In Synechococcus 7942, the replication of multi-copy chromosome is asynchronous, not only among cells but also among multi-copy chromosomes. This suggests that DNA replication is not tightly coupled to cell division in Synechococcus 7942. To address this hypothesis, we analysed the relationship between DNA replication and cell doubling at various growth phases of Synechococcus 7942 cell culture. Three distinct growth phases were characterised in Synechococcus 7942 batch culture: lag phase, exponential phase, and arithmetic (linear) phase. The chromosomal copy number was significantly higher during the lag phase than during the exponential and linear phases. Likewise, DNA replication activity was higher in the lag phase cells than in the exponential and linear phase cells, and the lag phase cells were more sensitive to nalidixic acid, a DNA gyrase inhibitor, than cells in other growth phases. To elucidate physiological differences in Synechococcus 7942 during the lag phase, we analysed the metabolome at each growth phase. In addition, we assessed the accumulation of central carbon metabolites, amino acids, and DNA precursors at each phase. The results of these analyses suggest that Synechococcus 7942 cells prepare for cell division during the lag phase by initiating intensive chromosomal DNA replication and accumulating metabolites necessary for the subsequent cell division and elongation steps that occur during the exponential growth and linear phases.
Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
Satoru
S
Watanabe
Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Saitama, 332-0012, Japan.
Ryudo
R
Ohbayashi
Genome Research Center, Tokyo University of Agriculture, Tokyo, Japan.
Yu
Y
Kanesaki
Institute for Advanced Biosciences, Keio University, Tsuruoka, Yamagata, Japan.
Natsumi
N
Saito
Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan.
Taku
T
Chibazakura
Institute for Advanced Biosciences, Keio University, Tsuruoka, Yamagata, Japan.
Tomoyoshi
T
Soga
Department of Bioscience, Tokyo University of Agriculture, Tokyo, Japan; Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency (JST), Saitama, 332-0012, Japan.
Hirofumi
H
Yoshikawa
D002876:Chromosomes, Bacterial / Q000235:genetics; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics; D055442:Metabolome; D046940:Synechococcus / Q000166:cytology / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism
D004269:DNA, Bacterial