Automobile fuel from E. coli
An article in the New Scientist caught my eye this morning, “Bacteria churn out first ever petrol-like biofuel,” which is a popular press summary of an article recently published in the Proceedings of the National Academy of Sciences. I’ve written about the challenges of using microorganisms as sources of biofuel previously, but the problems with using microorganisms are two-fold; first, the process is most useful if the organism can utilize a carbon source which is available in large amounts and is poorly degradable on its own such as cellulose, and second, the process should generate the most useful potential fuel product possible, and the organism should stop any further metabolism at that point. Ethanol is a common endpoint for many fermentation processes, and is something that is readily generated in large scale industrial processes. Unfortunately, biological production of ethanol as a fuel requires the further purification of the ethanol before it can be used, and the purification process uses energy as well limiting the net energy obtained in the procedure. Current production of other fuel additives by bacteria generate products that can be used in internal combustion engines, but not effectively, and they tend to degrade the engine over time. It would therefore be highly desirable to enable bacteria to biochemically synthesize hydrocarbon molecules which are identical to the ones used in petroleum-based fuels.
Researchers at the University of Exeter developed an artificial biochemical pathway in E. coli by introducing a number of genes from other microorganisms related to the synthesis of long chain hydrocarbons. E. coli on its own will produce long chain fatty acids, but these are not useful end products for use as a biofuel. Introducing genes related to fatty acid biosynthesis from two other bacteria, Photorhabdus luminescens (see this article for my story of this organism in a completely different context) and Nostoc punctiforme, which allowed E. coli to use its existing fatty acids to produce branched chain alkanes. Genes introduced from Cinnamomum camphor (a plant), and Bacillus subtilis (another bacterium) were used to enable E. coli to produce the fatty acids which were best able to enter the new pathway for forming fuel molecules.
The authors demonstrated by several analytic methods that production of industrially relevant long chain alkanes was accomplished by the introduction of these genes into E. coli. Future directions for the research are several fold. First, the process must be scaled up in order for it to be useful. Second, this process started with glucose as the initial carbon source, which is energetically costly to produce in itself. Third, the process laid out in the flow chart to the left is not terribly efficient; altering the expression of various components may force the pathway to be more efficient, but this leads to another problem. Long chain alkanes are extremely hydrophobic and will actively disrupt membranes they come into contact with. Organisms that produce these compounds would additionally need to be able to resist the effects of the toxic compounds they produce.
Posted on April 24, 2013, in Microbes in the News, Strange but True and tagged Escherichia coli, Exeter University, Fatty acid, Photorhabdus luminescens. Bookmark the permalink. Comments Off on Automobile fuel from E. coli.