PETpla.net Insider 07+08 / 2021

OUTER PLANET 54 PETplanet Insider Vol. 22 No. 07+08/21 www.petpla.net OUTER PLANET Bacteria transform terephthalic acid into vanilla flavouring Tasty transformation A recipe that starts with “Take one half of an empty PET bottle”? Although unlikely to happen, PET bottles have become the focus of attention for some scientists who managed to convert post-consumer bottles to vanillin. A decisive contribution to the miraculous transformation is made by the bacterium Escherichia coli (E. coli). Researchers from the University of Edinburgh have discovered that the bacterium E. coli, naturally found in the human and animal intestine, can be deployed as a sustainable way to convert post-consumer plastic into vanillin, a new study reveals. The sci- entists hope that their discovery could boost the circular economy, which aims to eliminate waste, keep products and materials in use and have positive impacts for synthetic biology. The scientists Joanna C. Sadler and Stephen Wallace from the Uni- versity of Edinburgh’s Institute of Quantitative Biology, Biochemistry and Biotechnology used a laboratory engi- neered E. coli bacterium to convert the monomer terephthalic acid (TA) directly into the high value molecule vanil- lin, via a series of chemical reactions, using a single engineered microorgan- ism. According to the researchers, the reaction is mild, uses a whole-cell catalyst produced from renewable feedstocks and occurs under ambi- ent conditions (room temperature, pH5.5–7), in aqueous media, requires no additional cofactors or reagents and generates no hazardous waste. Maxi- mum vanillin titres of 785 μ M (79% conversion) were achieved after exten- sive process optimisation studies. The team also demonstrated how the technique works by converting a used plastic bottle into vanillin by adding the E. coli to the degraded plas- tic waste at ambient temperature and in aqueous conditions: they therefore selected a thermostable enzyme as a biocatalyst to aid hydrolysis of PET into TA. This enzyme released TA directly and did not require an additional enzyme to hydrolyse mono-2-hydroxy- ethyl terephthalate (MHET) for release of TA. The reaction was cooled to room temperature and freshly prepared E. coli and a biotransformation buffer concentrate were added, and reac- tions were analysed after 24h. Without any process optimisation, vanillin was detected. The researchers say that the vanil- lin produced would be fit for human consumption but further experimental tests are required. Vanillin is widely used in the food and cosmetics indus- tries, as well as the formulation of herbicides, antifoaming agents and cleaning products. Global demand for vanillin was in excess of 37,000 t in 2018. The demand for vanillin is grow- ing rapidly and is projected to exceed 59,000 t by 2025. Natural vanillin can be produced by extraction and isola- tion from vanilla beans or rice bran. However, over 90% of the vanillin used worldwide is produced syntheti- cally - by microbial fermentation via a non-natural, engineered pathway. The aromatic substance Vanillin is a cheaper alternative to natural vanilla, whose prices had overtaken even the price of silver in recent years. Future studies will focus on inten- sifying this process through further strain engineering, process optimisa- tion and extension of the pathway to other metabolites. The study, published in Green Chemistry, lays the foundation for further studies to maximise vanil- lin production towards industrially relevant levels and the extension of the pathway to other metabolites. The research was funded by a BBSRC Discovery Fellowship and a UKRI Future Leaders Fellowship. www.ed.ac.uk www.rsc.org Vanillin can be extracted from natural ingredients like vanilla pods, which belong to the orchid family, or synthetically. This is where PET could join the game.