Metabolic engineering of Synechocystis sp. PCC6803 to produce astaxanthin

Astaxanthin is a carotenoid with wide applications because of its strong antioxidant properties. It is mainly produced from the green alga Haematococcus pluvialis, but large-scale production remains a challenge. To provide another source, here, Synechocystis sp. PCC6803 was adopted as the chassis cell, and its carotenoid biosynthesis pathway was genetically extended to produce astaxanthin. The beta-carotene ketolase gene (bkt) and carotenoid hydroxylase gene (crtR-B) from H. pluvialis, which wild-type Synechocystis sp. PCC6803 lacks, were optimized based on the codon preference of Synechocystis sp. PCC6803 and heterologously expressed in that bacterium to create a strain capable of producing astaxanthin. The Synechocystis sp. PCC6803 mutant synthesized 4.81 +/- 0.06 mg astaxanthin per gram of cells (dry weight) after nitrogen starvation for 14 days. More than 30% of the total astaxanthin was in the free form, and 82.61% was the strong antioxidant 3S, 3'S-astaxanthin isoform. These results show the industrial application potential of metabolically-engineered Synechocystis sp. PCC6803 for astaxanthin production.