Overexpression of bicarbonate transporters in the marine cyanobacterium sp. PCC 7002 increases growth rate and glycogen accumulation.

Background: sp. PCC 7002 is an attractive organism as a feedstock and for photoautotrophic production of biofuels and biochemicals due to its fast growth and ability to grow in marine/brackish medium. Previous studies suggest that the growth of this organism is limited by the HCO transport across the cytoplasmic membrane. Tools for genetic engineering are well established for this cyanobacterium, which makes it possible to overexpress genes of interest.

Results: In this work, we overexpressed two different native Na-dependent carbon transporters viz., SbtA and BicA in sp. PCC 7002 cells under the influence of a strong light-inducible promoter and a strong RBS sequence. The overexpression of these transporters enhanced biomass by about 50%, increased intracellular glycogen about 50%, and increased extracellular carbohydrate up to threefold. Importantly, the biomass and glycogen productivity of the transformants with air bubbling was even higher than that of WT cells with 1% CO bubbling. The overexpression of these transporters was associated with an increased carotenoid content without altering the chl content.

Conclusions: Our work shows the utility of increased carbon transport in improving the growth as well as product formation in a marine cyanobacterium and will serve to increase the utility of this organism as a potential cell factory.