311EFFECT OF VARIOUS CONCENTRATION OF CO2 ON PHOTOSYNTHETIC, RuBisCo AND CARBONIC ANHYDRASE ACTIVITY OF Synechococcus sp AND Phormidium spCO2 concentrating mechanism may improve the energetic efficiency and rate of carbon uptake in oxygenic photosynthetic organism. Cyanobacteria have evolved mechanisms to uptake and concentrate inorganic carbon from the environment. RuBisCo containing carboysomes, utilize CO2 generated from the accumulated Ci pool. Two cyanobacterial strains isolated from water bodies of Madurai namely Synechococcus sp and Phormidium sp strains were maintained in BG11 medium in different CO2 concentration such as 0.5%, 1%, 2%, 4%, 8% and 16%. Dry weight was maximum in Synechococcus sp strain than in Phormidium sp. Chlorophyll a and protein was maximum in 4% CO2 concentration in Synechococcus sp. Increased carbon dioxide levels in the atmosphere and its influence on climate change is a growing concern in the scientific, political, and social communities. Methods of mitigation are being tested to explore carbon capture and storage through the biosynthesis of stable carbon-containing compounds using different strains of cyanobacteria. Rate of photosynthesis and rate of respiration was greater in low CO2 concentration in both Synechococcus sp and Phormidium sp. Amount of RuBisCo, assay of RuBisCo and carbonic anhydrase activity was greater in high concentration of CO2 in Synechococcus sp. Total protein profile in different CO2 concentrations was monitored in 12% SDS – PAGE. SEM analysis of carboxysomes confirmed the icosahedral nature of the protein. The potential for the sustainable deployment of algae as a means of capturing carbon sources globally. The study indicates the cyanobacteria are efficient fixers of high concentration of carbondioxide.s_srisudha2006@rediffmail.comResearch4112013Cyanobacteria,CO2 Sequestration,RuBisCo,carbonic anhydrase,CarboxysomeMeenakshi S,Srisudha SResearch Centre in Botany and Microbiology, Lady Doak College, Madurai – 625002. Tamilnadu, India.,Research Centre in Botany and Microbiology, Lady Doak College, Madurai – 625002. Tamilnadu, India.