Gram-scale production of 4-vinyl guaiacol in the fast-growing phototrophic cyanobacterium Synechococcus sp. PCC 11901

Abstract

Whole-cell catalysis in cyanobacteria allows the transformation of light energy into chemical energy by co-factor recycling and in situ production of oxygen by photosynthesis, requiring only light, CO<inf>2</inf>, water, and a few minerals. Despite these benefits, cyanobacteria have not been deployed on a large scale due to low yields, comparably slow growth, and low biomass accumulation. Additionally, previous works on whole-cell catalysis in cyanobacteria indicate higher yields at high CO<inf>2</inf> concentrations, highlighting the need for a source of inorganic carbon to balance photosynthesis and prevent photorespiration. Here, we addressed these problems by combining a fast-growing, high biomass-accumulating strain, Synechococcus sp. PCC 11901, with a CO<inf>2</inf>-releasing enzymatic reaction, a phenolic acid decarboxylase. After identifying the product toxicity as the limiting factor, we were able to achieve a final product concentration of 80 mM from ferulic acid to 4-vinyl guaiacol with a two-phasic system with diisononyl phthalate and also describe the first use with cyanobacteria of the environmentally benign alternative isopropyl myristate, thus converting a lignin-derived waste product into a valuable precursor molecule for bioplastics and fragrances. We were able to scale the reaction up by employing an inexpensive cultivation system to a final yield of 1.19 g (97% yield) with 100 mL cell suspension and a simple extraction method. This configuration could enable continuous, photosynthetic oxygen production during large-scale cyanobacterial whole-cell catalysis without requiring the addition of an external carbon source.