Intensive DNA Replication and Metabolism during the Lag Phase in Cyanobacteria

Abstract

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.

Relative stability of ploidy in a marine Synechococcus across various growth conditions

“…The relative stability of chromosome copy number in Synechococcus sp. WH7803 during growth is similar to that observed in the oligoploid freshwater cyanobacterium Synechococcus elongatus PCC 7942 (Griese et al, 2011), which also shows an increase in ploidy at the end of the lag phase (Watanabe et al, 2015). In contrast, the Archaea Halobacterium salinarum and Halovorax volcanii and the freshwater cyanobacterium Synechocystis sp.…”

Comparative Genomics of DNA Recombination and Repair in Cyanobacteria: Biotechnological Implications

“…The well-studied strain Synechocystis PCC6803 has a 3.57 Mb chromosome, with a 48% GC content (http://genome.microbedb.jp/cyanobase/) and a copy number of 10–50 (Labarre et al, 1989; Griese et al, 2011). For the other models the values are 2.69 Mb, 55% and 2–5 for Synechococcus PCC7942 (Mann and Carr, 1974; Griese et al, 2011; Watanabe et al, 2015); and 3.00 Mb, 50%, and likely 2–5 for Synechococcus PCC7002 (Griese et al, 2011; Watanabe et al, 2015). Synechocystis PCC6803 also has seven plasmids, ranging from 2.3 Kb (Chauvat et al, 1986) to 119vKb (http://genome.microbedb.jp/cyanobase/); Synechococcus PCC7942 has one plasmid (46 Kb); and Synechococcus PCC7002 has seven plasmids (4.8–186 Kb).…”

The ploidy level of Synechocystis sp. PCC 6803 is highly variable and is influenced by growth phase and by chemical and physical external parameters

“…For example, in the archaeon Halobacterium salinarum the copy number decreased from 25 in the exponential phase of growth to 15 in the stationary phase (Breuert et al, 2006). Growth-phase-dependent ploidy level changes have also been analysed for another cyanobacterium, Synechococcus elongatus PCC 7942 (Watanabe et al, 2015). A culture was pre-incubated in the dark for 18 h and then transferred to light conditions to enable photosynthetic growth.…”