Researchers at The University of Manchester, Imperial College London and University of Turku have made an advance toward the renewable biosynthesis of propane with the creation of a new synthetic pathway in E. coli, based on a fermentative butanol pathway. An open access paper on the work is published in the journal Biotechnology for Biofuels.
In 2014, members of the team from Imperial College and the University of Turku had devised a synthetic metabolic pathway for producing renewable propane from engineered E. coli bacteria, using pathways based on fatty acid synthesis. (Earlier post.) Although the initial yields were far too low for commercialization, the team was able to identify and to add essential biochemical components in order to boost the biosynthesis reaction, enabling the E. coli strain to increase propane yield. Yields, however, were still too low.
The authors [of the earlier study] concluded that the pathway was limited by total flux through fatty acid synthesis (FAS). The most obvious example of this limitation comes from the markedly enhanced rate of propane synthesis observed when fatty acids were supplied to the external media. In the present study, we sought to bypass this limitation by generating new synthetic pathways that are not dependent on FAS. In this study, we designed a series of modified butyraldehyde pathways based on the CoA-dependent butanol pathways commonly found in Clostridium spp. Propane biosynthesis was thereafter achieved by interrupting the route to alcohol by the addition of ADO.—Menon et al.
The team led by Nigel Scrutton from Manchester and Patrik Jones from Imperial College modified existing fermentative butanol pathways using an engineered enzyme variant to redirect the microbial pathway to produce propane as opposed to butanol.
In the study, the researchers assembled and evaluated four different synthetic pathways for the production of propane and butanol. The most efficient of these produced propane wit a yield of 220 ± 3 μg/L. By deleting competing pathways and then including a previously designed variant with an enhanced specificity towards short-chain substrates and including a ferredoxin-based electron supply system, the team increased the propane titre to 3.40 ± 0.19 mg/L.
This study focused on the construction and evaluation of alternative microbial biosynthetic pathways for the production of renewable propane. It also expands the metabolic toolbox for renewable propane production, providing new insight and understanding of the development of next-generation biofuels which one day could lead to commercial production.—Professor Nigel Scrutton, co-corresponding author
This study was funded by the European Union and involved scientists from the BBSRC/EPSRC Centre for Synthetic Biology of Fine and Speciality Chemicals based at the Manchester Institute of Biotechnology, in collaboration with the University of Turku in Finland and Imperial College, London.
Navya Menon, András Pásztor, Binuraj RK Menon, Pauli Kallio, Karl Fisher, M Kalim Akhtar, David Leys, Patrik R Jones and Nigel S Scrutton (2015) “A microbial platform for renewable propane synthesis based on a fermentative butanol pathway” Biotechnology for Biofuels 8:61 doi: 10.1186/s13068-015-0231-1