Cell-free styrene biosynthesis at high titers

Abstract

Styrene is an important petroleum-derived molecule that is polymerized to make versatile plastics, including disposable silverware and foamed packaging materials. Finding more sustainable methods, such as biosynthesis, for producing styrene is essential due to the increasing severity of climate change as well as the limited supply of fossil fuels. Recent metabolic engineering efforts have enabled the biological production of styrene in Escherichia coli, but styrene toxicity and volatility limit biosynthesis in cells. To address these limitations, we have developed a cell-free styrene biosynthesis platform. The cell-free system provides an open reaction environment without cell viability constraints, which allows exquisite control over reaction conditions and greater carbon flux toward product formation rather than cell growth. The two biosynthetic enzymes required for styrene production were generated via cell-free protein synthesis and mixed in defined ratios with supplemented L-phenylalanine and buffer. By altering the time, temperature, pH, and enzyme concentrations in the reaction, this approach increased the cell-free titer of styrene from 5.36 {+/-} 0.63 mM to 40.33 {+/-} 1.03 mM, an order of magnitude greater than cellular synthesis methods. Cell-free systems offer a complimentary approach to cellular synthesis of small molecules, which can provide particular benefits for producing toxic molecules. HighlightsA cell-free system for styrene biosynthesis was established. This in vitro system achieved styrene titers an order of magnitude greater than the highest reported concentration in vivo.