Organic solvent-tolerant bacteria as a host for whole-cell biocatalysis: Enzymatic dehydration of aldoximes in organic medium

Aldoxime dehydratase (Oxd) is an heme-dependent enzyme that catalyzes the dehydration of aldoximes to produce nitriles, offering a sustainable alternative to conventional chemical synthesis. Herein, we report the development of a whole-cell catalytic system using the organic solvent-tolerant bacterium Rhodococcus erythropolis L88 as a host for the expression of Oxd. Unlike conventional biocatalytic systems under aqueous conditions, this system enables efficient aldoxime dehydration in hexane, thereby overcoming solubility limitations of hydrophobic substrates and eliminating laborious extraction steps, which simplifies reaction work-up. Importantly, R. erythropolis cells expressing Oxd from Bacillus sp. OxB-1 exhibited excellent catalytic efficiency, affording the desired octanenitrile in 92% yield. In contrast, an E. coli-based whole-cell catalyst used as a benchmark showed negligible activity, revealing the robustness of the solvent-tolerant Rhodococcus host. Furthermore, the presented whole-cell catalytic system was successfully applied to preparative-scale synthesis of structurally diverse nitriles. Considering the robustness, scalability, and compatibility with hydrophobic substrates, the R. erythropolis-based system would serve as a sustainable platform for nitrile production.