Influence of carbon-dioxide on the growth of Spirulina sp. (MCRC-A0003) isolated from Muttukadu backwaters, South India.

Growth of Spirulina sp. (MCRC-A0003), a cyanobacterium, was evaluated under different concentrations of carbon-dioxide (CO2) (4-50 %) in a closed glass photobioreactor. Although significant CO2 utilization by the cyanobacterial strain was observed up to 50 % concentration, complete utilization was observed only at 4, 10 and 20 % concentrations on 3rd, 6th and 8th day respectively. However, considerable reduction was witnessed in reactors containing 30-50 % CO2 only between 6th and 9th day. A corresponding increase in the biomass and primary metabolites like chlorophyll-a, carbohydrate and protein were observed. Biomass productivity of Spirulina in reactors sparged with 4, 10 and 20 % CO2 were 13.7, 43 and 44 % more than that in control reactor without CO2. While CO2 increased the levels of primary metabolites in the cyanobacterial cells, it was quite prominent in 10 % CO2 concentration with the chlorophyll-a, carbohydrate and protein contents were 64, 183 and 626 mg g(-1) respectively. While 10 and 6.6 % increase were noticed in chlorophyll-a and protein, 17 % increase in carbohydrate levels was observed in Spirulina cells, which could be attributed to the conversion of CO2 to carbohydrate by the cyanobacterium.