Lightwave 2

At the end of each 24 h step of light increment, 22 ml of culture were harvested to perform in parallel dry weight measurements and cell size analysis.
For the determination of dry cell weight, cellulose acetate membranes (0.2 μm, Whatman, Maidstone, United Kingdom) were washed with milli-Q water (Merck Millipore Reference, Burlington, MA, United States), left to dry for 24 h at 90 °C in a stove (Electrolux, Stockholm, Sweden) and weighted with an analytical balance (AB204; Mettler Toledo, Columbus, OH, United States). Subsequently, the membranes were used for filtering 20 ml of sampled culture. After washing once with milli-Q water to remove salts, the membrane filter was left to dry overnight in the stove at 90 °C and finally weighted again. In parallel, the OD₇₃₀ of the sampled cells was measured with a spectrophotometer (Lightwave II; Biochrom, Cambridge, United Kingdom) and used to normalize the dry cell weight per OD₇₃₀.
The average cell size and cell number were measured with the CASY counter instrument (Roche Applied Science, Penzberg, Germany). A volume of 20 μl of harvested culture was diluted with 10 ml of CASY ton solution. The average cell size was measured working in a range of calibration between zero and five μm with a capillary of 60 μm.

All molecular cloning procedures were carried out in E. coli DH5α, either grown on solidified LB plates, containing 1.5% (w/v) agar, or in liquid LB medium at 37 °C in an incubator with a shaking speed of 200 rpm. When appropriate, antibiotics were added to the medium for propagation of specific plasmids. Concentrations of antibiotics used, alone or in combination, were 100 µg mL⁻¹ for ampicillin and 50 µg mL⁻¹ for kanamycin.
A glucose-tolerant Synechocystis derivative was obtained from D. Bhaya, University of Stanford, Stanford, CA. Normally, it was cultivated in BG11 medium [37 ] at 30 °C in a shaking incubator at 120 rpm (Innova 43, New Brunswick Scientific) under constant moderate white light illumination, ~ 30 μmol photons m⁻² s⁻¹, measured with an LI-250 light meter (LI-COR, Inc). For Synechocystis mutant construction, kanamycin or nickel sulfate was added to the medium with a final concentration of 50 µg mL⁻¹ or 20 µM, respectively. Biomass concentration in the cultures was monitored by recording the optical density at 730 nm (OD₇₃₀) in a spectrophotometer (Lightwave II, Biochrom).