Effects of alkalinity, extremely low carbon dioxide concentration and irradiance on spectral properties, phycobilisome, photosynthesis, photosystems and functional groups of the native cyanobacterium Calothrix sp. ISC 65

Calothrix sp. ISC 65 was characterized physiologically by combination of extremely low irradiance (2 ~kE m-2 s-1), different alkalinity (pH 7, 9, 11), and extremely limited carbon dioxide concentration (no aeration, no carbon dioxide enrichment). Spectroscopical analysis showed that, after 96 hours, pH 9 caused a significant increase in growth rate, chlorophyll, and phycocyanin production. A lower one (pH of 7) caused a decrease of phycobilisome production even after 24 hours. Excitation of the light harvesting complex and the reaction center of photosystems resulted from pH of 9. Phycocyanin seems to be the main part of phycobilisome but pH 9 caused phycoerythrin and allophycocyanin production excitation in the outer part of the photosynthetic antenna as well. A fluorimetric and photosynthesis-irradiance curve analysis showed that increasing alkalinity (up to pH 9) caused an increase in photosynthesis efficiency and a decrease of non-photochemical fluorescence especially after 96 hours. PSII : PSI ratio increased by increasing alkalinity from pH 7 to 9 and reached the highest level after 96 hours. Surface response plot analysis showed that there is a narrow border line around pH 9 and 96 hours, which caused the highest PSII : PSI ratio. FTIR analysis showed that alkalinity caused configuration changes of the functional groups. The difference of the functional group patterns between pH 7 and 11 was significant especially after 24 hours. Differences in asymmetric carbon vibration, lipid stretching and OH bending of the polysaccharides occurred with both pH 9 and 11 treatments. pH 9 caused the most physiological activities in Calothrix sp. ISC 65 at extremely limited irradiance and carbon dioxide concentration.