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

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±7.5Umg^-1, 23.2±2.8Umg^-1, and 10.9±1.2Umg^-1 were achieved after 6-9h 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 150mM styrene oxide to phenylacetaldehyde was observed for the enzyme StyC-Kp5.2 indicating a significantly improved stability towards product inactivation. Remarkably, more than 300mM product (>36gL^-1, yield of about 80%) were finally synthesized from 400mM substrate with 150U of this enzyme within 60-120min. This represents the highest product concentration which has been reached with this type of enzymes, so far.