In summary, the study has revealed that substituted phenylacetic acids can in principal be produced from correspondingly substituted styrenes by means of suitable styrene-degrading bacterial isolates which harbor enzymes of the side-chain oxygenation. 4-chlorostyrene turned out to be a well suited co-metabolic substrate and in particular, it was most efficiently converted by P. fluorescens ST. Considerable differences were also observed in the enantioselective potential of the initial degradation pathway relevant in the conversion of α-substituted styrene analogs. Again, strain ST showed highest specificity and an enantiomeric excess of 40% was determined for the (S)-4-chloro-α-methylphenylacetic acid. The remarkable ability of a Gordonia-isolate to convert 4-isobutyl-α-methylstyrene into ibuprofen demonstrates a novel route towards this drug. However, a biotechnological application of these strains requires further optimization approaches to improve the product yields.