Improving trans-cinnamic acid production in a model cyanobacterium.

trans-Cinnamic acid (tCA) is a precursor in the synthesis of many high-value compounds with bio-active qualities useful in applications like medicine, polymers, and cosmetics. Currently tCA is produced by industrial chemical synthesis from fossil fuels or cost-prohibitive isolation from terrestrial plants. Cyanobacteria, a type of photosynthetic bacteria, can be readily engineered to convert sunlight and carbon dioxide into metabolites of interest at relatively high amounts compared to terrestrial plants. The purpose of this study is to advance the industrial and commercial value of cyanobacteria as a biological factory for renewable production of tCA. Production of tCA has previously been demonstrated in the model cyanobacterium Synechocystis sp. PCC 6803 (S. 6803) via expression of non-native phenylalanine ammonia lyase (PAL) from various organisms. This project focuses on developing and characterizing a new high-titer strain of S. 6803 expressing a plant PAL gene controlled by an inducible promoter. We assessed production in shake flasks under constant light, a 12 h:12 h light:dark cycle, and environmental photobioreactors (ePBRs) with a sinusoidal, rapidly fluctuating light environment. Our strain demonstrates a four-fold increase in tCA production to ~500 mg L-1 by 14 days compared to previously reported titers in S. 6803 under shake flask cultivation and a 30-50% improved average tCA production per culture density (60 mg·L-1·OD730 -1) in ePBRs over comparable previously reported culture methods. Our study progresses S. 6803 tCA bioproduction into higher culture volumes, up to 500 mL, while further validating the strength of an inducible system for tCA production in S. 6803.