Recombinant Escherichia coli Utilizes Mild Hydrogen Sources for the Targeted Intracellular Synthesis of Palladium Nanoparticles and Whole-Cell-Catalyzed Aromatic Aldehyde Hydrogenation.

Metal-enzyme cascade catalysis effectively combines the broad reactivity of chemical catalysis with the high selectivity of biocatalysis, improving reaction efficiency and simplifying the process flow through multiple sequential reactions in the same system. The introduction of exogenous palladium nanoparticles (Pd NPs) into Escherichia coli (E. coli) cells can significantly broaden the range of catalytic reactions facilitated by biological enzymes. Additionally, the targeted cytoplasmic synthesis of Pd NPs enhances their utilization efficiency in intracellular catalytic reactions while also eliminating the need for separating and purifying metals and enzymes. However, current methods largely enable the intracellular synthesis of Pd NPs in the periplasmic space and outer membrane. Moreover, the hydrogen sources commonly used in these methods─such as hydrogen (H₂) and sodium borohydride (NaBH₄)─carry safety risks. In this study, the mechanism of targeted synthesis of Pd NPs on the cytoplasmic side and its process were deeply investigated using a mild hydrogen source, sodium formate, in combination with genetic engineering and preparation conditions. And the constructed functional cell (Pd@E. coli) could catalyze benzaldehyde hydrogenation, with a conversion rate of 41.41% and benzyl alcohol yield of 17.68%, demonstrating considerable catalytic and loading stability. This study provides a reference for constructing catalytic systems for intracellular metal-enzyme cascades. Thus, it could bolster the development opportunities in the areas of non-natural products and drug development and provide ideas for addressing the drawbacks of existing biosynthetic technologies.