Figure 4.

Viable cell counts, total cell numbers and PHB contents of mineral salts medium-grown R. eutropha H16 and R. eutropha ΔphaC cells during incubation in PBS. Cells were grown in mineral salts medium supplemented with 1% of sodium gluconate for 10 h as described in ‘Materials and methods’, harvested by centrifugation and then suspended in MSM without a carbon source and incubated at 30°C (red line) or at 5°C (blue line). Wild type cells (solid lines) had ∼33% accumulated PHB. At indicated points of time, viable cell counts [cfu ml⁻¹] (A and B), total number of cells [cells ml⁻¹] and PHB content [% of cellular dry weight (cdw), mean of two determinations] (C) were determined. In (A), the time scale of the first 24 h is enlarged relative to the time scale of 3 weeks in (B). The same log scale of 5 decades is given in all graphs for better comparability. Examples of microscopical images of Nile red-stained wild type cells (overlay of bright field image and fluorescence image) are shown in (D). Note, the shortening of the cells and decrease in the number of red-stained PHB granules after 21 days at 30°C but not at 5°C. Error bars indicate standard deviation. PHB contents of the phaC mutant were not determined because the inability to synthesise PHB in the absence of PHB synthase has been frequently reported.