Researchers at LS9 have discovered an alkane biosynthesis pathway in cyanobacteria; i.e., a metabolic pathway that produces alkanes—the major hydrocarbon constituents of gasoline, diesel and jet fuel—in a direct, simple conversion from sugar.
When the newly identified alkane operon is expressed in E.coli, the bacteria produce and secrete C13 to C17 mixtures of alkanes and alkenes. This discovery is the first description of the genes responsible for alkane biosynthesis and the first example of a single step conversion of sugar to fuel-grade alkanes by an engineered microorganism. A paper on the work was published in the 30 July issue of the journal Science.
Alkanes are naturally produced by diverse species, but the genetics and biochemistry behind this biology have not been well generally well understood. The LS9 team looked into the genomes of cyanobacteria that produce alkanes in nature, evaluating many and identifying one that was not capable of producing alkanes, said Andreas Schirmer, Associate Director of Metabolic Engineering at LS9, and lead author on the paper. By comparing the genome sequences of the alkane producing and non-producing organisms, LS9 was able to identify the responsible genes.
The pathway consists of an acyl–acyl carrier protein reductase and an aldehyde decarbonylase, which together convert intermediates of fatty acid metabolism to alkanes and alkenes. The aldehyde decarbonylase is related to the broadly functional nonheme diiron enzymes.
…The genes and enzymes described here provide a foundation for the deeper understanding and further development of this pathway. The ability to biologically convert renewable carbohydrate selectively to fuel-grade alkanes without hydrogenation is an important step toward the goal of low-cost renewable transportation fuels.
—Schirmer et al.
LS9 says that the discovery is consistent with its focus on developing renewable petroleum products using a proprietary one-step fermentation process that significantly reduces the costs and energy inputs. While other biological routes to the production of renewable hydrocarbons are emerging, these other routes require costly and energy intense chemical conversion technologies such as distillation or hydrogenation, LS9 notes.
This is a one step sugar-to-diesel process that does not require elevated temperatures, high pressures, toxic inorganic catalysts, hydrogen or complex unit operations. We believe in simple processes at LS9, and the simplicity of this process has allowed us to successfully accelerate its scale-up and development.
—Steve del Cardayre, Vice President of Research and Development
In addition to alkanes, LS9 is scaling-up its production of a biodiesel product and a portfolio of chemicals used in making industrial and consumer products.
In January, a collaboration led by researchers with the US Department of Energy’s Joint BioEnergy Institute (JBEI) and including LS9 announced the engineering of a strain of Escherichia coli bacteria to produce biodiesel fuel and other important chemicals derived from fatty acids. (Earlier post.)
Andreas Schirmer, Mathew A. Rude, Xuezhi Li, Emanuela Popova, Stephen B. del Cardayre (2010) Microbial Biosynthesis of Alkanes. Science Vol. 329. no. 5991, pp. 559 – 562 doi: 10.1126/science.1187936