Heterologous production of different styrene oxide isomerases for the highly efficient synthesis of phenylacetaldehyde

- Heterologous production of three styrene oxide isomerases was performed.
- The yield of these enzymes was significantly enhanced.
- A high stability towards product inactivation was determined for StyC-Kp5.2.
- StyC-Kp5.2 enhances the reachable product concentrations by a factor of 4.
- More than 36 g L−1 phenylacetaldehyde (yield of 80%) were produced within 60 min.

The styrene oxide isomerase (SOI, StyC) represents a key enzyme of the styrene-degrading pathway and has been discussed as promising biocatalyst during recent studies. The enzyme enables the synthesis of pure phenylacetaldehyde from styrene oxide. In this study the native as well as the corresponding codon-optimized genes of three different SOIs from Rhodococcus opacus 1CP (StyC-1CP), Sphingopyxis fribergensis Kp5.2 (StyC-Kp5.2), and Pseudomonas fluorescens ST (StyC-ST) were investigated for the expression in Escherichia coli BL21(DE3)pLysS. Specific enzyme activities of 61.9 ± 7.5 U mg−1, 23.2 ± 2.8 U mg−1, and 10.9 ± 1.2 U mg−1 were achieved after 6-9 h for the codon-optimized gene of strain 1CP and the native genes of Kp5.2 and ST, respectively. Afterwards, these enzymes were enriched and applied for biotransformation studies. A complete conversion of 150 mM styrene oxide to phenylacetaldehyde was observed for the enzyme StyC-Kp5.2 indicating a significantly improved stability towards product inactivation. Remarkably, more than 300 mM product (>36 g L−1, yield of about 80%) were finally synthesized from 400 mM substrate with 150 U of this enzyme within 60-120min. This represents the highest product concentration which has been reached with this type of enzymes, so far.