Synergistic Effects of Light and Salinity on Carotenoid and Biomass Composition of Synechocystis PCC6803 Cultures

Light and salt stress affect the growth of plants and microorganisms, causing photo-oxidative stress. The cyanobacterium <i>Synechocystis</i> is notable for its adaptability to and sustainability in seawater. In this study, the synergistic effects of different light intensities and salt concentrations on the growth and biomass composition of <i>Synechocystis</i> were examined. Cultures were grown in BG11 medium (control) and with 20 and 40 g L^-1 marine salts (obtained from a commercial sea water preparation) at 100, 200, and 400 μmoles photons m^-2 s^-1 (LL, ML, and HL, respectively) to assess the interactive effects of salinity stress and increasing light intensity. The effect of salinity stress was most pronounced under LL and ML, where the highest accumulation of all major carotenoids was observed; under HL, the contents of most carotenoids significantly increased mainly at the highest salt concentration but to a lesser extent). Under LL and ML echinenone reached the highest values (2.71-fold and 3.75-fold higher than in the control, respectively), whereas β-carotene showed the highest increase at LL, reaching concentrations three times those of the control. At HL myxoxanthophyll exhibited the highest increase with marine salt (1.9-fold higher than in the control). The results show that <i>Synechocystis</i> could grow at all light intensities and marine salt concentrations via increased synthesis of carotenoids in response to physiological stress.