Biological technologies are important in the production of many types of products, and will become increasingly important in future, for several reasons: (1) Much conventional manufacturing relies on energy and/or chemicals generated from fossil carbon resources, but there is an urgent need to transition to environmentally and economically sustainable circular economies in order to decrease greenhouse gas emissions, limit climate change and limit environmental degradation. Biological technologies can provide sustainable alternatives. (2) Biological technologies are, or could be, superior to conventional non-biological methods of producing some types of products, because they provide important advantages in the efficiency, costs, and control over some types of chemical reactions. (3) Biologically active chemicals are important in medicine, nutrition and agriculture, all of which are actively growing and developing areas in which many new products can be expected. Biological technologies often have advantages in production of these types of chemicals. (4) The transition to sustainable circular economies and development of the above types of products represent huge economic opportunities for advanced, high-tech economies like the UK, the US and EU to develop, exploit and export the technologies that will be required. This project is focused on a new product called ketone ester and two key chemical precursors used in its production, called (R)-3-hydroxybutyrate (R3HB) and (R)-1,3-butanediol (R13BD). Ketone ester is a 'nutraceutical'. Nutraceuticals are a class of products consumed as nutritional supplements, but which provide additional benefits beyond regular food or nutrients, of the kind more commonly associated with pharmaceuticals, hence the term nutraceutical. Development and commercialisation of ketone ester is the focus of University of Oxford spin-out company TdeltaS. TdeltaS has performed many studies showing that ketone ester is safe to consume as a drink, and once inside the body is quickly broken down into natural 'ketone bodies' with beneficial effects. Ketone bodies are exceptional sources of energy, and are especially good at providing energy to the brain and blood. Ketone bodies are naturally found in the human body, but are only usually made during starvation or during special diets which can cause health problems. Consumption of ketone ester provides a rapid, safe and convenient way to obtain the benefits of ketone bodies, and studies have found benefits in enhancing athletic performance, in defence, and the potential to treat various diseases. Crucially, ketone ester has regulatory approval and has already reached a high-value market as a consumer nutraceutical in the US. Great demand for ketone ester, particularly from athletes, has rapidly outstripped supply. Developing a reliable UK supply of R3HB and R13BD as chemical precursors for ketone ester would improve the scale of production and commercial success of ketone ester, allowing the market to grow to reflect the great demand. R3HB and R13BD also have many other uses as chemicals in other industries, with established markets. The chemical structures of R3HB and R13BD mean they can be very effectively produced by biotechnological means. This project's industrial partner, CHAIN Biotechnology, has previously generated engineered microbial strains which produce R3HB and R13BD, but only in mixtures with other products, which does not suit the current aim. The overall aim of this project is to apply the combined expertise, experience and capacity of the academic applicants and industrial partner CHAIN Biotechnology to develop new strains of microorganisms which produce R3HB and/or R13BD well enough that they could be used to manufacture these chemicals. The project will also demonstrate production of the ketone ester itself in engineered cells, which could lead to a simpler biomanufacturing process for ketone ester in future.