Outdoor semi-continuous cultivation of Synechococcus sp. for enhanced carotenoid production

The carotenoid productivity of a euryhaline Synechococcus sp. was studied in indoor and outdoor conditions. Indoor experiments revealed that the strain could maintain growth and carotenoid accumulation within a salinity range of 2.5–8.0 % NaCl. In an indoor two phase semi-continuous cultivation in PBRs, every three days, 50 % of the culture was replaced with fresh growth media in phase one, whereas the removed culture was grown for another three days in the second phase to enhance the carotenoid yield. Biomass and carotenoid productivity of the strain in the second phase were similar in five consecutive cultivation cycles. Next, the same two-phase cultivation experiment was conducted in 5 sq. m outdoor raceway tanks. However, for the outdoor experiment, carotenoid-rich biomass was harvested from the second phase by membrane filtration, and the growth media was recycled for cultivating in the first phase. The salinity of the culture continued to increase as the evaporated water was balanced by seawater. The semi-continuous cultivation of the first phase continued for 20 days before the culture salinity reached 7.4 % NaCl. For Synechococcus sp., the growth and carotenoid productivities were not affected within this salinity range.