Influence of luminosity, carbon source and concentration of salts in the physiology of Chlorella sorokiniana.

Growth studies are important to increase the knowledge about the physiology of microalgae. The development of suitable culture media allows optimum growth to each species. The genus Chlorella has the ability to adapt to various environmental and nutritional conditions. Thus, the aim of this work was to evaluate the physiology of Chlorella sorokiniana CTT 7727 at different growth conditions with Basal Bold (BB) medium. For that, heterotrophic, autotrophic and mixotrophic cultures were carried out. The maximum specific growth rates (µmax ), the maximum biomass concentrations (Xmax ) and cell productivities (PX ) were calculated for each experiment. Among all the treatments evaluated, that with 24 h light, 3x BB (g L-1 ) and CO2 presented a higher µmax (0.40 day-1 ) and maximum cell concentration due the increased concentration of nutrients. Replacement of dark to light has increased Xmax from 2.3 × 105 to 9.3 × 106 cells mL-1 in regular BB medium and 3.6 × 105 to 2.1 × 107 cells mL-1 in 3x BB medium in autotrophic cultivations. The PX increased from 2.4 × 104 cells mL-1 h-1 (1x BB (g L-1 )) to 3.6 × 104 cells mL-1 h-1 (3x BB (g L-1 )), in the presence of 24 light and CO2 . However, the same behaviour was not observed when BB concentration was increased 6, 8 or 10 times the initial concentration of BB medium. Experiments with pulses of concentrated nutrients showed that declining cells can resume their growth after nutrient depletion, but the viability is decreased after successive pulses.