, 1996). Stationary phase cells also contained 3–4 genomes per cell. Therefore, in S. elongatus, the ploidy www.selleckchem.com/products/epacadostat-incb024360.html level is not growth phase-regulated, in contrast to many other species. The results of genome quantification for Synechococcus WH7803 are also summarized in Table 1. This species also contained between three and four genome copies at an OD750 nm of 0.6 and during stationary phase, and is thus oligoploid. Again, this is in accordance with

an earlier study that applied FACS analysis for genome copy number determination and found 2–4 copies per cell (Binder & Chisholm, 1990). Taken together, the freshwater as well as the salt water species were found to be oligoploid, irrespective of the applied method for quantification (based either on www.selleckchem.com/Proteasome.html one specific site of the genome (this study) or the average DNA content), growth in continuous light (this study) or growth in light–dark cycles (Mori et al., 1996), and the growth phase. First, the motile Synechocystic PCC 6803 wild-type strain was analyzed. An average growth curve of three independent cultures is shown

in Fig. S3. The results of genome copy number determination are summarized in Table 2. The doubling time at the cell harvest in linear growth phase (OD750 nm = 0.6) was around 20 h. Synechocystis PCC 6803 turned out to be highly polyploid, and it contained nearly 60 genomes per cell, both in linear and in stationary growth phase. As this value is very high and in fact higher than any value published until now for any cyanobacterial species, the genome copy number in stationary phase cells was also determined using an independent method, namely spectroscopic determination of the DNA concentration. The average values of 57.9 Thymidine kinase (if the plasmid copy number would be low) and 53.3 (if the plasmid copy number would be high) genomes per cell were in excellent agreement with the real time PCR result, and thus underscored that Synechocystis PCC 6803 is highly polyploid. An earlier study had also shown that this species is polyploid, but the reported value of 12

genome copies per cell for the ‘Kazusa’ wild-type of Synechocystis PCC 6803 (Labarre et al., 1989) is much lower than the value determined in this study. The reason for the discrepancy is not obvious, as in the previous study also the lysis efficiency was quantified, genome size was underestimated by only 32%, and the colorimetric assay for DNA quantification probably cannot be that wrong. The same medium was used, and a similar doubling time of 15–20 h was reported. Therefore, it might be that both reports are correct and that the ploidy level of various strains of the species Synechocystis PCC 6803 are different. To test this hypothesis, another wild-type strain of Synechocystis PCC 6803 was used, i.e. the so-called GT wild-type.