Using genetic engineering to increase production of phycocyanin, a blue pigment in cyanobacteria

Phycocyanin is a major protein component of the light-harvesting antenna in many cyanobacteria.  It is comprised of two protein subunits covalently bound to a blue pigment called phycocyanobilin. Phycocyanin is used as a natural food dye, and is known to be an antioxidant. To increase the intracellular content of this valuable product, we built a strain of Synechococcus elongatus (Se) PCC 7942 that carried an extra copy of the genes encoding the two phycocyanin subunits, and found that this strain contained a higher concentration of phyocycanin regardless of the growth conditions. To extend this finding to a production strain of cyanobacteria, we developed an approach to genetically manipulate Arthrospira platensis (Spirulina). Our new technology allows for genetically engineering Spirulina to constitutively express transgenes.  Using this technology, we integrated an additional copy of the phycocyanin genes into its chromosome by targeted homologous recombination. Similarly to what we observed in Se PCC 7942, the resulting Spirulina strain overexpressed the phycocyanobilin-bound proteins, showing that increased gene dosage can increase the phycocyanin content of cyanobacteria. This study illustrates that we can translate results in a model cyanobacteria to a commercially useful production strain.