Figure 1.

Eukaryotic‐like DNA synthesis: flow cytometric analysis of the DNA content of Gram‐negative Sphingomonas sp. LB126 cultivated for 60 h. The species was grown aerobically at 20 °C and pH 7.5 in 500 mL shake flasks with 300 mL minimal medium at 150 r.p.m. The carbon and energy source was glucose (1 g/L). The harvested cells were centrifuged at 3200 g for 5 min, fixed with 10% NaN₃, and stored at 4 °C. Bacterial DNA was stained by treatment of 2 mL of diluted cell suspension (3 × 10⁸ cells per millilitre) with 1 mL solution A (2.1 g citric acid/0.5 g Tween 20 in 100 mL bidistilled water) for 10 min. Afterwards the cells were washed and re‐suspended in 2 mL solution B (0.24 µm 4′,6‐diamidino‐2‐phenylindole [DAPI, SIGMA], 400 mm Na₂HPO₄, pH 7.0) for at least 20 min (according to Shi et al. 2007). Flow cytometric measurements were carried out using a MoFlo cell sorter (DakoCytomation, Fort Collins, CO, USA) equipped with two water‐cooled argon‐ion lasers (Innova 90C and Innova 70C from Coherent, Santa Clara, CA, USA). Chromosome equivalents are presented as C_1n and C_2n. Uncoupled DNA synthesis: The Gram‐negative Escherichia coli K12 was grown aerobically at 30 °C and pH 7.5 for 24 h in 500 mL shake flasks at 150 r.p.m. on 300 mL peptone media (L): 5 g peptone from meat (pancreatic), 3 g NaCl, 2 g K₂HPO₄, 10 g meat extract, 10 g yeast extract, 5 g glucose. The staining procedure and device equipment was the same as above though the DAPI concentration was enhanced to 0.5 µm DAPI within solution B. Chromosome equivalents are presented as C_1n and C_2n. Uncoupled DNA synthesis is shown to be performed between the 7th and 14th hours.