Fig. 4

Biomass productivity of WT and std1 Chlamydomonas cells measured in photobioreactors operated as turbidostats during photoautotrophic N deprivation. Cells were grown under constant illumination (125 µmol photons m⁻² s⁻¹) in the presence of 2 % CO₂ enriched air. Cell density was measured using an absorption probe and maintained at a constant level by injection of fresh medium. Due to the aggregation phenotype of std1, OD_880nm was regulated at different values for WT (OD_880nm = 0. 4) and std1 (OD_880nm = 0. 3) to reach similar biomass concentrations (0. 15 g dry weight L⁻¹). After a 48-h stabilization period in the presence of MM, the dilution medium was replaced by MM-N (t ₀). a Cumulated amounts of fresh medium were added to maintain the culture at a constant biomass concentration. Measurements of ammonium concentration (dotted lines) in the culture medium showed complete exhaustion after 45 h. The 100 % value corresponds to 7.5 mM NH₄ ⁺, which is the ammonium concentration of the minimal medium. Shown are mean ± SD (n = 3). b Biomass productivity (g dry weight L⁻¹ d⁻¹) was determined from dilution rates and biomass measurements at t ₀, and 48 and 72 h after N-removal. Shown are means ± SD (n = 3)