Engineering synthetic pathways to bio-ethylene production in Cupriavidus necator

Background: Ethylene is currently produced from stream cracking of ethane which produces large quantaties of CO2, contributing to global warming. In 2000, steam cracking had a primary energy use of 3 billion Gigajoules and accounted for approximately 200 millions tons of CO2 emissions. Ethylene is the monomer for the most common plastic, polyethylene, and annual global production is approximately 80 million tons. Finding a sustainable or carbon neutral alternative to ethylene production is imperative. Cupriavidus necator is a gram-negative soil bacterium, capable of growing on CO2 and H2 enabling low carbon fuels and chemicals to be produced with minimal release of CO2 to the environment. Research in this area is at the forefront of the green revolution and the production of bio-ethylene from sustainable or carbon neutral sources further spearheads a diminished reliance on fossils fuels throughout the world.

Aim: The aim of this project is to engineer Cupriavidus necator as a platform for the production of hydrocarbon-based products such as ethylene. As proof of concept, we have expressed the efe genes (ethylene forming enzyme) from P. syringae pv. paseolicola, which is sufficient for ethylene production in heterologous hosts and Ralstonia solanacearum. We have generated ethylene from minimal media and from CO2; and we are now in the process of improving production through directed evolution and metabolic engineering. As part of this process we would like to engineer a synthetic pathway for ethylene production utlising the Yang pathway from plants. This provides an exciting opportunity to implement a novel pathway in C. necator and link ethylene production to growth. Ethylene is efficiently biosynthesized from 1-aminocyclopropane-1-carboxylic acid (ACC) (Zhou et al., 2002), which is itself derived from methionine as a branch of the Yang cycle (Wang et al., 2002). This process is energetically efficient as it preserves the high-energy methionine thioether bond. This pathway utilises SAM synthtase, ACC synthase and ACC oxidase. The conversion of 1-amino-cyclopropane-1-carboxylic acid (ACC) to ethylene releases cyanoformic acid, which spontaneously decarboxylates to release cyanide, which is principally detoxified by the CAS pathway (machingura et al., 2016). The implementation of this pathway will provide a mechanism for detoxifiying cyanide in C. necator.

Training: The project will allow for training in a unique multidisciplinary environment, incorporating genomic engineering, gas fermentation, synthetic biology, cutting edge molecular biology and systems biology modelling. The project will provide the student with a vast array of transferable skills, highly prized by employers in the growing bioeconomy. The project will also provide several high impact publications. This translational project will be carried out within the BBSRC/EPSRC Synthetic Biology Research Centre (SBRC) at Nottingham which comprises 70+ graduate and postdoctoral researchers (www.clostron.com/people.php) and a current budget of £27M.