P26: Solving problems with product toxicity in bioproduction of styrene

Styrene is a large volume commodity chemical which is used as precursor for a range of useful polymers and co-polymers. The conventional styrene synthesis is performed through dehydrogenation of petroleum-derived ethylbenzene. Recently, styrene synthesis from renewable resources has been reported, involving the biocatalytic conversion of endogenous L-phenylalanine to styrene by expressing Arabidopsis thaliana phenylalanine ammonia lyase (PAL2) and Saccharomyces cerevisiae trans-cinnamate decarboxylase (FDC1) in engineered microorganisms. The main limiting factor for the biosynthesis is the toxicity of the product. Styrene toxicity was estimated to be around 3 mM and, at present, production titres much higher than this threshold have not been reported. This makes the sustainable route uneconomic compared with the chemical counterpart. In our research we aimed to overcome the toxicity issues by using in situ product recovery based on two approaches: extraction into biocompatible ionic liquids in a biphasic system and the utilization of an ion-exchange resin for adsorption. [P _{6 6 6 14}] [Tf₂N] and [N _{1 8 8 8}] [Tf₂N] showed different extraction efficiencies but in the presence of either, Escherichia coli was able to grow with unprecedented levels of styrene. When Amberlite XAD-4 was used as the adsorbent resin, it led to rapid, complete removal of styrene and allowed E. coli to grow almost normally. We have also tested a hypothetical trans-cinnamate decarboxylase (OHBA1) from Aspergillus niger as an alternative enzyme for styrene biosynthesis. Its activity in catalysing the conversion of trans-cinnamic acid to styrene has been confirmed and compared to the already reported FDC1.