Styrene is a versatile commodity petrochemical and important monomer compound whose global demand is expected to surpass 41 million tons by 2020, representing a &gt;$28 billion market in the U.S. alone. Currently, all commercially available styrene is derived from non-renewable petroleum feedstocks. Recently, however, microorganisms including Escherichia coli and Saccharomyces cerevisiae have been engineered to produce styrene directly from biomass sugars. However, just as with many other hydrocarbon products, styrene is inhibitory to its producing microorganisms are relative low concentrations. E. coli, for example, is completely inhibited in the presence of just ~200-300 mg/L styrene. Thus, end-product toxicity currently constitutes the principal bottleneck limiting microbial styrene production. One proven, process-based strategy for enhancing the net biosynthesis of and inhibitory chemical product involves the integration of effective separation mechanisms for its selective removal from the culture media as its forms to thereby preclude its ability to accumulate to toxic levels. In this study, two strategies were systematically investigated and compared for the in situ removal of styrene from cultures of engineered E. coli, namely solvent extraction and gas stripping. In solvent extraction, from a pool of initial candidates it was ultimately determined that the addition of bis(2-ethylhexyl)phthalate offered the greatest productivity enhancement, allowing net volumetric production of 836 ± 64 mg/L to be reached, representing a 320% improvement over single phase cultures. Gas stripping rates, meanwhile, were controlled by rates of bioreactor agitation and, to a greater extent, aeration. A periodic gas stripping protocol ultimately enabled up to 561 ± 15 mg/L styrene to be attained. Lastly, by relieving the effects of styrene toxicity, new insight can be gained regarding subsequent factors that limit its biosynthesis in E. coli and strategies for future strain improvement are discussed.

Comparing In situ removal strategies for improving styrene biosynthesis

249th National Meeting (2015)

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