Culturing Synechocystis sp. PCC 6803

Synechocystis sp. PCC 6803 was used in all experiments apart from the glucose experiments, which were carried out with the glucose-tolerant strain Synechocystis sp. PCC 6803-GT. Cultures were grown at 30°C with photoperiod 18-h/6-h light/dark, light intensity 120 ± 15 μmol photons/m²/s and sparged with humidified ambient air. 20 ml cultures were set up from glycerol stocks maintained at -80°C and gradually scaled up to 1.5 L cultures in Bijou bottles with a working volume of 60–75% of the bottle capacity. Cultures were grown in full BG11 medium (Stanier et al. 1971 (link)) for control conditions, in BG11 with 12.5% of the specified nutrients for low nutrient conditions (Madsen et al. 2021 (link)) or in BG11 with 300 mM NaCl or glucose added. For low light conditions, light intensity was reduced to 35 or 80 μmol photons/m²/s. Growth was monitored by measuring optical density at 730 nm (OD₇₃₀) in a Lambda 45 UV/VIS Spectrophotometer (PerkinElmer, Waltham, MA, USA). To ensure measurements were performed in the linear range of the spectrophotometer, cultures were diluted in fresh media to OD <1, the sample OD was measured, and the culture OD was calculated by multiplying the sample OD with the respective dilution factor.