Getting E. coli to make propane

Apparently some scientists have made propane in a lab with little more than the bacteria in our guts: E.coli.

This is interesting for a number of reasons. It would make propane produced in this way a renewable fuel. You don’t hear the words renewable and propane together in a sentence very often! It’s also a synthetically produced fuel that does not compete with food in the way crop-based biofuels do.

It works like this: E.coli produces fatty acids to make cell membranes. If a special enzyme called thioesterase is introduced during this process of cell membrane synthesis, these fatty acids will produce butyric acid instead. Butyric acid — aside from smelling like vomit — is also a precursor for propane.

What’s not clear to me is whether propane produced in this way is carbon-neutral. Presumably carbon is absorbed during this process and then released again when it is burnt. If inputs = outputs then I guess it is carbon-neutral but I’m really not sure. If anyone knows the answer to this then please let me know.

Here’s the media release from Imperial College –

The paper is available here –

11 thoughts on “Getting E. coli to make propane

  1. Biogas digesters are promoted strongly in developing countries. The farmers fuel the digester with cow manure normally, and through anaerobic fermentation, methane is produced and piped to the kitchen for use in gas burners. Quite common in India, Indonesia and many other countries in Asia.

  2. Interesting post. A renewable fuel is always worth trying. I was thinking about cow manure and methane when I read your article. Having read the comments, why do I find it perfectly all right to use methane produced by cow manure, but when I think of people poop I go “Eeuw!” It’s all the same process after all! 🙂

    1. Cow poop is less offensive than our own, I do agree. Perhaps this is because our own poop can so easily make us sick and so we have evolved to find it particularly unpleasant.

    1. I wonder if the farm is still powered in this way. Do you know? It would be a shame if developing countries shifted away from using this as a form of energy in the same way that we did.

  3. From Fig 1 of the paper, the fuel for this synthesis seems to be glucose (a hydrocarbon). It would include the carbon sequestered by the creation of sugars in the source flora. The resulting propane reduces, when burnt, to CO2 and H2O. Hence the CO2 is recycled and the total process effectively carbon neutral.

    However, as far as I can determine, glucose/sugars can only be produced by the photosynthesis of plants. Either directly and/or by the hydrolysis of starches. So, land space is required.

    Overall, the initial conversion to glucose is sunlight driven and probably requires as much light on the leaf (ground space) as any other bio-fuel for the equivalent amount of energy. The only advantage may be that this can done using any plant not just fermented seed grain. Therefore, if inedible plants where grown in places where nothing else would grow, this might have some use. Unfortunately, even if such a case existed, I do not think it would still be any more than a small part of a solution. However, it’s all grist to the mill and a good job in distributing the information.

    Incidentally, you seem to have metamorphosed from a squirrel. I’m going to have to change the the all ports warning. “No longer has bushy tail”. 😀

    1. Thanks, Graham. An article in Carbon Brief makes the same point as you.

      At the moment the propane-producing bugs are fed glucose, a simple sugar. The energy in the sugar has to come from somewhere – probably sugar cane. The sugar cane takes land to grow, energy to harvest and process and so on.

      The researchers say the bacterial machinery that makes the propane could be put inside cyanobacteria, also known as blue-green algae. The algae wouldn’t need glucose to grow, just sunlight and some basic nutrients like carbon dioxide, nitrogen and phosphorus. That would mean you could turn sunlight into propane.

      But whether you use glucose from sugar cane or photosynthetic algae, the energy ultimately comes from the sun, and that is where the fundamental limitations of the idea begin to bite.

      Although I don’t really get why using cyanobacteria isn’t a good solution.

      1. Theoretically it, and other bio-fuels from the sea, are good solutions. The practical problem is the low yield. All present hydrocarbon sources and fossilized sources were created by the sun’s energy. The fossil hydrocarbons being highly concentrated. Even uranium was created in the heart of stars. It is probably better that we go direct to the source e.g. solar panels, solar furnaces, wind, tide, wave, geothermal and hydro. I see two main problems.

        1. Photovoltaic type solar cells are woefully inefficient.
        2. All of the green energy sources, except geothermal and hydro, are inconstant and the energy needs to be stored. The best means of storage and fuel for vehicles is hydrogen. Splitting water by electrolysis is, at present, also inefficient. The best method is only about 75% and is slow and requires a lot of expensive plant.

        If science can improve the efficiency of using cleanly produced electricity to extract hydrogen from water, then all the pieces would be in place and the engineers could get on with the job.

        Just a note: Whilst algae would not need glucose to grow, it must have a hydrocarbon content (which it does) produced by photosynthesis. No hydrocarbon, no propane.

        And another: Growing plants for this purpose would be carbon neutral but using existing flora/fauna would just release sequestered carbon.

        The whole issue has so many factors that it is difficult to determine the best route. There are often many plans that can work. From those, the one that does work is the one that we all get behind and make it work. :-).

        Upon that approach, I shall now gather all my parts and head for sleep. A big day tomorrow. Fifty tall ships from around the world are gathering on the Thames quite near me and there will be a 4 day festival. You won’t be hearing from me for a while. 🙂

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