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Sustainable production of styrene from renewable sources

More than labwork

Our team did not only design the project and performed many hours of labwork and modelling over the summer, we also thought about how our project fits into society. Safety, public engagement and education, entrepeneurship, engaging in constructive debates with stakeholders and interviewing experts on their thoughts about our project design played an important role as well. Next to all partners from industry and academia, we also collaborated with other iGEM teams and met at several meetups! Besides all the efforts we still managed to have an amazing summer. We want to thank all of our sponsors, the donors on our crowdfunding page and all the people that have helped us to make our project a succes!

Our challenge

The production of many chemicals is currently based on fossil fuels. Fossil fuels are however a finite resource which the world is using rapidly. Models indicate that oil resources will be depleted in the next couple of decades [1]. Hence, there is an ever increasing attention for replacement with bio-renewable resources and sustainable production processes. We believe that the transition away from fossil fuels towards a bio-based economy is one of the key challenges of the 21st century. Therefore, our iGEM team decided to contribute to a sustainable future and a greener planet by investigating a bio-based alternative production route for the important chemical styrene.

Styrene

The monomer styrene is the basis of the industrial production of many plastic polymers, including Acrylonitrile Butadiene Styrene (ABS), Styrene Butadiene rubber or crosslinked polystyrene. Styrenes apolar, aromatic structure lets these materials obtain highly desired physical, chemical and electrical properties which cannot be reached with other materials. Styrene can be viewed as a versatile compound that is processed into numerous applications, which range from LEGO blocks to industrial rubbers, bike tires or isolation materials in electronic devices. The thermoplastic properties of many of these plastics also make them easier to recycle. Over the last 70 years styrene products have become ubiquitous in our daily lives and irreplaceable for many industries, which is why the demand for styrene will inevitably outlast the availability of fossil fuels. The development of an alternative, sustainable production route is therefore of utmost importance.

StyGreen

With the advances in synthetic biology, we can nowadays use microbes to produce a large range of chemicals, which is a powerful technology to address the great challenges of our time. We therefore investigated the possibility to produce styrene with microbes. Styrene has a large structural similarity to phenylalanine, which is commonly present in living organisms, indicating that this makes a suitable precursor in a pathway towards styrene production by microbes. In fact, styrene production by microbes is highly feasible [2]. Therefore, we aim to make styrene in a sustainable manner by engineered microorganisms, a product we dubbed StyGreen.

Renewable resources

To make StyGreen sustainable, it is of importance that the input into our process is a bio-renewable source of feedstock. Therefore, the final step is the need for a suitable input on which our StyGreen-producing microbes can grow. There are many possibilities that may serve as feedstocks for our cells, but we decided to seek for bio-based waste streams with low value specifically, which we can turn into the valuable StyGreen product. Microorganisms grow well on sugars and a high number of waste streams contain large amounts of sugar in the form of glucose polymers which are known as cellulose. Therefore, we investigated bio-renewable waste streams containing cellulose and evaluated them by multiple technical, financial, economical and ecological criteria.

A greener future

We aim to create a consolidated bioprocessing system by combining all necessary steps to convert cellulose into styrene in one single microorganism: the yeast Saccharomyces cerevisiae. The StyGreen molecules that we produce can subsequently be used in all types of conventional industrial processes concerning non-single use plastics. In this manner, we simultaneously ensure sustainable styrene availability and a green planet for future generations.

References

[1] Shafiee, S., & Topal, E. (2009). When will fossil fuel reserves be diminished? Energy Policy, 37(1), 181–189. http://doi.org/10.1016/J.ENPOL.2008.08.016

[2] McKenna, R., Thompson, B., Pugh, S. & Nielsen, D. R. Rational and combinatorial approaches to engineering styrene production by Saccharomyces cerevisiae. Microb. Cell Fact. 13, 123 (2014).