Strain and process engineering to exploit solvent tolerance mechanisms of Pseudomonas taiwanensis VLB120 for asymmetric styrene epoxidation

To reduce the environmental burden associated with chemical production processes and the dependency on limited fossil resources, whole-cell biocatalysis is considered a promising sustainable alternative to existing processes. However, the typically apolar character of target compounds often compromises biocatalyst efficiency due to inhibitory or toxic effects on the applied enzymes and microorganisms. In this thesis, solvent-tolerant P. taiwanensis VLB120 was evaluated as a biocatalyst to improve the economic and ecological performance of asymmetric (S)-styrene oxide production. Biocatalyst as well as reaction and process engineering was applied, considering critical aspects as well as potential synergies resulting from differences in native and technical environments and design objectives. The constitutively solvent-tolerant regulatory mutant P. taiwanensis VLB120∆C∆ttgV was constructed as a means to avoid the necessity for unproductive solvent-adaptation phases. This constitutive solvent tolerance resulted in a doubling of the specific styrene epoxidation activity of resting cells. The application of cells growing under glucose excess conditions resulted in the highest specific styrene epoxidation rates (180 U gCDW-1) reported for a process-relevant two-liquid phase biotransformation setup. The constitutive solvent tolerance of P. taiwanensis VLB120∆C∆ttgV allowed a reduction in extractive organic phase volume by up to 90%, which previously has been identified as environmentally and economically critical. Thorough characterization of the interaction of glucose metabolism and solvent tolerance allowed the definition of further biocatalyst and process design objectives and engineering strategies.