Metabolic engineering of Synechocystis sp. PCC 6803 for the production of aromatic amino acids and derived phenylpropanoids

In light of the climate change challenge, the advantageous trait of using solar energy and carbon dioxide to produce organic molecules has granted cyanobacteria deserved interest as hosts for metabolic engineering. Importantly, these organisms do not directly compete with agricultural resources. Aromatic amino acids and derived phenylpropanoids are of high importance because they are used by the pharmaceutical, food, cosmetic, and agricultural industries as precursors of active ingredients. Amino acids are traditionally produced by extraction from protein hydrolysates, chemical synthesis or fermentation pathways using heterotrophic microorganisms. In this work we demonstrate for the first time the efficient overproduction of phenylalanine and tyrosine from CO2 in a Synechocystis sp. PCC 6803 strain heterologously expressing the feedback-inhibition-resistant AroG and TyrA enzymes from E. coli. Production titers reached 904 +/- 53 mg/gDW (580 +/- 34 mg/L) of phenylalanine and 64 +/- 3.7 mg/gDW (41 +/- 2.3 mg/L) of tyrosine after 10 days of photoautotrophic growth. We estimate that the production of the two amino acids corresponds to 56% of the total fixed carbon. Phenylalanine and tyrosine are the precursors for phenylpropanoids, thus, we tested the functionality of several phenylpropanoid biosynthetic enzymes in the generated cyanobacterium strains and successfully achieved the production of 470 +/- 70 mg/gDW (207 mg/L) of p-coumaric acid, 267 +/- 31 mg/gDW (114 mg/L) of cinnamic acid and 47.4 +/- 13.9 mg/gDW (12.6 mg/L) of caffeic acid after 6 days of photoautotrophic growth. All compounds were secreted to the growth medium. Our work enlarges the repertoire and yield of heterologous chemicals produced by Synechocystis and contributes to extend the molecular knowledge about this cyanobacterium.