Chlorophyll fluorescence induction and relaxation system for the continuous monitoring of photosynthetic capacity in photobioreactors.

The development of high-performance photobioreactors equipped with automatic systems for non-invasive real-time monitoring of cultivation conditions and photosynthetic parameters is a challenge in algae biotechnology. Therefore, we developed a chlorophyll (Chl) fluorescence measuring system for the online recording of the light-induced fluorescence rise and the dark relaxation of the flash-induced fluorescence yield (Qa- - re-oxidation kinetics) in photobioreactors. This system provides automatic measurements in a broad range of Chl concentrations at high frequency of gas-tight sampling, and advanced data analysis. The performance of this new technique was tested on the green microalgae Chlamydomonas reinhardtii subjected to a sulfur deficiency stress and to long-term dark anaerobic conditions. More than thousand fluorescence kinetic curves were recorded and analyzed during aerobic and anaerobic stages of incubation. Lifetime and amplitude values of kinetic components were determined, and their dynamics plotted on heatmaps. Out of these data, stress-sensitive kinetic parameters were specified. This implemented apparatus can therefore be useful for the continuous real-time monitoring of algal photosynthesis in photobioreactors.