Abstract
BackgroundSynechococcus 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 HCO3− transport across the cytoplasmic membrane. Tools for genetic engineering are well established for this cyanobacterium, which makes it possible to overexpress genes of interest.ResultsIn this work, we overexpressed two different native Na+-dependent carbon transporters viz., SbtA and BicA in Synechococcus 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% CO2 bubbling. The overexpression of these transporters was associated with an increased carotenoid content without altering the chl a content.ConclusionsOur 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.
Highlights
IntroductionPasteur culture collection (PCC) 7002 cells under the influence of a strong light-inducible promoter and a strong ribosome binding sites (RBS) sequence
Cyanobacteria are attractive organisms for the production of biofuels, biomass and other bioproducts due to their ability to carry out photosynthesis as well as their genetic tractability [1]
There are three major types of bicarbonate transporters in cyanobacterial cells, which differ in their affinity to H CO3−/CO2: (a) BCT1, an ATP-binding cassette (ABC) transporter, a medium affinity low flux transporter that was the first reported bicarbonate transporter [9], (b) the sodium-dependent bicarbonate transporter A, an inducible, high affinity, low flux transporter Sbt A, and (c) the bicarbonate transporter Bic A, a constitutive, low affinity, high flux transporter
Summary
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. Cyanobacteria are attractive organisms for the production of biofuels, biomass and other bioproducts due to their ability to carry out photosynthesis as well as their genetic tractability [1]. PCC 7002 under Ci-limiting conditions, indicating that these genes play a major role in Ci uptake [10] Both SbtA and BicA are sodium-dependent active bicarbonate transporters that require about 1 mM N a+ for their half-maximal HCO3− transport activity [11, 12]. The knock-out of both sbtA and bicA genes showed significantly reduced bicarbonate transport and slower growth at pH 9.3 [12]
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