Photosynthetic monitoring techniques indicate maximum glycogen accumulation in nitrogen-limited Synechocystis sp. PCC 6803 culture

Abstract

Chlorophyll fluorescence and oxygen evolution are rapid and non-invasive monitoring techniques to obtain information about the photosynthesis performance of microalgae cultures. These methods may be employed for optimizing the biomass productivity as well as indicate increased production of some valuable compounds.In this work photosynthesis monitoring techniques – saturation pulse analysis of fluorescence quenching, fast fluorescence induction kinetics and photosynthetic oxygen production/respiration – were employed for monitoring of the physiological state of the nitrogen-limited culture of Synechocystis sp. PCC 6803. The correlation between changes of photosynthetic activities, growth and glycogen accumulation was examined in these cultures. The aim was to determine proper point for biomass harvest comparing the changes of photosynthetic activities and the kinetics of glycogen accumulation. In a 4-day trial the highest glycogen accumulation in biomass was found on day 2 showing an inflection point which was accompanied by the reversal of the chlorophyll fluorescence variables, namely maximal photochemical efficiency of PSII Fv/Fm, relative electron transport rate rETR, photochemical efficiency α and photosynthesis saturating irradiance Ik. The rapid increase of cell respiration after day 2 also indicated the relation of these changes with onset of glycogen catabolism.Our laboratory experiments revealed that the three photosynthetic monitoring techniques provided good indication of the physiological changes leading to high glycogen accumulation in biomass of the nitrogen-limited Synechocystis culture. In this way the glycogen accumulation can be manipulated. The photosynthesis measurements can indicate the right time to harvest the culture rich in glycogen in biotechnological applications.