Harnessing photosynthetic bacterium for light-powered biocatalysis

The traditional whole-cell biocatalysis typically utilizes the heterotrophic microbes as the biocatalyst, which requires carbohydrates to power the cofactor (ATP, NAD(P)H) regeneration. In this study, we sought to harness purple non-sulfur photosynthetic bacterium (PNSB) as the biocatalyst to achieve light-driven cofactor regeneration for cascade biocatalysis. We substantially improved the performance of PNSB-based biocatalysis by using a highly active and conditional expression system, blocking the side-reactions, controlling the feeding strategy, and attenuating the light shading effect. We found that 50 mM ferulic acid could be completely converted to vanillyl alcohol in the recombinant strain, reaching 7.7 g/L vanillyl alcohol. In addition, >99.9% conversion of p-coumaric acid to p-hydroxybenzoic alcohol (6.21 g/L) was similarly achieved under light-anaerobic conditions. Moreover, we examined the isoprenol utilization pathway (IUP) for pinene synthesis and 13.81 mM pinene (1.88 g/L) with 92.1% conversion rate from isoprenol was obtained. Taken together, these results suggested that PNSB could be a promising host for light-powered biotransformation, which offers an efficient approach for synthesizing value-added chemicals in a green and sustainable manner.