Fundamental Insight and Biotechnological Optimisation to Enable Commercial Production of Renewable Propane

Propane, a short chain alkane used as a combustible fuel, has a well-established global market. Recently, novel synthetic pathways have been described for the biological production of propane. Though these are currently not yet commercially viable, a genuinely renewable source of propane would alleviate some of our current dependence on unsustainable fossil fuels.

Together with BDS Fuels and University of Manchester (Nigel Scrutton group) we have identified an opportunity to develop renewable propane production as a complement to existing natural gas systems. However, in order to implement renewable propane production commercially the process needs to first be improved.

Pathways for alkane biosynthesis converge on the terminal step where aldehydes are converted to alkanes. This reaction can be catalysed by cyanobacterial Aldehyde Deformylating Oxygenase (cADO) using iron and oxygen to remove a formate molecule from an aldehyde substrate producing hydrocarbon product. However, the catalytic activity of cADO is very low and therefore this step is limiting carbon flux to propane. Whilst efforts to improve the specificity of the cADO binding pocket towards short chain substrates through rational engineering have already improved titres of hydrocarbon products, efficient utilisation of butyraldehyde would require further optimisation.

Biological production of renewable propane on a commercial scale requires three aspects to be addressed; first, improving our understanding of the native system and increasing the function of cADO and therefore also increasing the production of alkanes, either directly or by developing a more favourable environment. Secondly, enhancing flux to alkane precursors and finally, the scale up and implementation of renewable propane biosynthesis.

This project will study the alkane biosynthetic system in its native environment in order to understand and potentially also utilise new insight for application. We estimate that at least a 10-fold increase in carbon flux from sugar to propane is required for commercial viability. Competing pathways utilising the same substrates can be deleted. However, this can have negative implications for the overall metabolic balance of the cell. Metabolic network modelling could provide insight into the impact of pathway alterations. When combined with systematic investigations into down regulation of a library of variants using CRISPR interference, modelling could be used to help move towards an optimal balance. Protein and waste product analysis can be used to verify the functionality of variants and data generated can be fed back and used to test the efficacy of models.

Engineered strains will be evaluated at lab and pilot scale in collaboration with the University of Manchester and BDS Fuels.