Improving Biotransformation Efficiency of Arthrobacter simplex by Enhancement of Cell Stress Tolerance and Enzyme Activity.

Arthrobacter simplex exhibits excellent Δ1-dehydrogenation ability, but the acquisition of the desirable strain is limited due to lacking of comprehensive genetic manipulation. Herein, a promoter collection for fine-tuning gene expression was achieved. Next, the expression level was enhanced and directed evolution of the global transcriptional factor (IrrE) was applied to enhance cell viability in systems containing more substrate and ethanol, thus contributing to higher production. IrrE promotes a stronger antioxidant defense system, more energy generation, and changed signal transduction. Using a stronger promoter, the enzyme activities were boosted but their positive effects on biotransformation performance were inferior to cell stress tolerance when exposed to challenging systems. Finally, an optimal strain was created by collectively reinforcing cell stress tolerance and catalytic enzyme activity, achieving a yield 261.8% higher relative to the initial situation. Our study provided effective methods for steroid-transforming strains with high efficiency.