Multidimensional optimization for accelerating light-powered biocatalysis in Rhodopseudomonas palustris

Background: Whole-cell biocatalysis has been exploited to convert a variety of substrates into high-value bulk or chiral fine chemicals. However, 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. Results: 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 Rhodopseudomonas palustris -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 770.8 mg/g-cdw vanillyl alcohol. In addition, > 99.9% conversion of p -coumaric acid to p -hydroxybenzyl alcohol (620.7 mg/g-cdw) was similarly achieved under light-anaerobic conditions. Moreover, we examined the isoprenol utilization pathway (IUP) for pinene synthesis and 188 mg/g-cdw pinene with 92% conversion rate from 30 mM isoprenol was obtained. Conclusions: Taken together, these results suggested that R. palustris 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.