Metabolic engineering of cyanobacteria for photosynthetic 3-hydroxypropionic acid production from CO2 using Synechococcus elongatus PCC 7942

Abstract

Photosynthetic conversion of CO2 to chemicals using cyanobacteria is an attractive approach for direct recycling of CO2 to useful products. 3-Hydroxypropionic acid (3 HP) is a valuable chemical for the synthesis of polymers and serves as a precursor to many other chemicals such as acrylic acid. 3 HP is naturally produced through glycerol metabolism. However, cyanobacteria do not possess pathways for synthesizing glycerol and converting glycerol to 3 HP. Furthermore, the latter pathway requires coenzyme B12, or an oxygen sensitive, coenzyme B12-independent enzyme. These characteristics present major challenges for production of 3 HP using cyanobacteria. To overcome such difficulties, we constructed two alternative pathways in Synechococcus elongatus PCC 7942: a malonyl-CoA dependent pathway and a β-alanine dependent pathway. Expression of the malonyl-CoA dependent pathway genes (malonyl-CoA reductase and malonate semialdehyde reductase) enabled S. elongatus to synthesize 3 HP to a final titer of 665 mg/L. β-Alanine dependent pathway expressing S. elongatus produced 3H P to final titer of 186 mg/L. These results demonstrated the feasibility of converting CO2 into 3 HP using cyanobacteria.

Biological Production of 3-Hydroxypropionic Acid: An Update on the Current Status

“…After modifications by genetic engineering, the recombinant strains are also capable of producing 3HP through CO 2 fixation by the Calvin cycle, and further transformation to phosphoenolpyruvate, which can be converted to 3HP by two newly developed pathways, namely the malonyl-CoA intermediate pathway and the β-alanine intermediate pathway [64,65]. n.a.…”

“…The newly constructed strain was capable of producing approximately 0.84 g/L 3HP directly from CO 2 . The malonyl-CoA route was also used by Lan et al [65] for the construction of a recombinant Synechococcus elongatus strain. The authors expressed the mcr gene from Sulfolobus tokodaii and the malonate semialdehyde reductase gene (msr) from Metallosphaera sedula, which resulted in the production of 0.67 g/L of 3HP.…”

“…Oxaloacetate is transformed by the action of aspartate transaminase to aspartate, which is then converted to β-alanine by the action of aspartate carboxylase. Finally, β-alanine is converted to malonate semialdehyde by the action of β-alanine aminotransferase, and finally, to 3HP by the action of malonate semialdehyde reductase [65]. Lan et al [65] constructed this pathway in S. elongates cells by expressing the phosphoenolpyruvate carboxylase gene (ppc) and the aspartate aminotransferase gene (aspC) from E. coli, together with the β-alanine aminotransferase gene (SkPYD4) from Saccharomyces kluyveri and the msr gene from M. sedula.…”

“…Finally, β-alanine is converted to malonate semialdehyde by the action of β-alanine aminotransferase, and finally, to 3HP by the action of malonate semialdehyde reductase [65]. Lan et al [65] constructed this pathway in S. elongates cells by expressing the phosphoenolpyruvate carboxylase gene (ppc) and the aspartate aminotransferase gene (aspC) from E. coli, together with the β-alanine aminotransferase gene (SkPYD4) from Saccharomyces kluyveri and the msr gene from M. sedula. Production of 3HP from CO 2 was approximately 0.19 g/L, which was lower than the results obtained when 3HP was produced through the malonyl-CoA intermediate pathway.…”

Cyanobacteria: Promising biocatalysts for sustainable chemical production

“…The product titers improved when the culture was subjected to phosphate starvation (48). 3-hydroxypropionic acid (3-HP) has been produced from malonyl-CoA via two successive reductions with malonate semialdehyde as an intermediate (54). The authors also introduced a parallel pathway to 3-HP via β-alanine in order to avoid the feedback-regulated synthesis of malonylCoA from acetyl-CoA (54).…”