Fuel from E. coli
Via @AnP_prof and NBC News, this is a cool story about an advance in molecular engineering of E. coli to enable this bacterium to produce propane. The news alert points to a publication in the journal Nature Communications, describing research from scientists from the University of Turku in Finland, and University College London. I’ve talked about work using microbes to make fuels in several capacities (see here, here, here, and here for some examples), and the primary challenge is to enable it to be a process that is sufficiently efficient to make it worthwhile from an energetic, and a financial standpoint.
The main issue with using bacteria to make hydrocarbon-based fuel is that they are both very hydrophobic, and as a result are toxic to cells. Forcing a cell to produce these compounds then can create a situation where the cell is essentially poisoning itself. Additionally, other attempts to engineer biosynthetic pathways for fuel production generate products that require some amount of additional purification before use, which means additional financial expense and energy expenditure prior to having a usable product. The current research, although it is in the preliminary stages and currently only has generated small amounts of propane, has regardless produced fuel that can be used in an engine essentially immediately.
The scientists took advantage of an existing pathway in E. coli that synthesizes membranes–the hydrophobic barrier that surrounds all cells–and interrupted it. Membrane precursors were shuttled into an alternative pathway that produced propane in just a few steps. To accomplish this, they introduced specific genes from at least 5 other bacterial species into E. coli, in order to construct the biochemical pathway for the synthesis of propane. The novelty of the approach is that no pathway to generate propane had been identified in any prokaryotic species. The scientists propose at the conclusion of their study several approaches for optimizing the process in order to scale it up for industrial production. One direction they suggest is to transfer the synthetic pathway into a photosynthetic microorganism, which naturally accumulates many of the additional enzyme substrates (NADPH and reduced ferredoxin) in the pathway from the figure.
There are several advantages for propane as a terminal product; it makes up the bulk of liquid petroleum gas, which is extensively used in cars, home heating systems, and elsewhere, and propane easily switches between a liquid and a gaseous state at ambient conditions. This latter property means that it can be easily removed from a culture vessel, diminishing the toxic effects that it would have on the cells that produce it. Once it has been released and collected, it can then be easily returned to a liquid state, which facilitates storage and transport. The group anticipates that with successful scale up, this process may produce fuel for vehicles within the next 5 to 10 years.