Running on bacteria: E. Coli & biofuels
This week, a paper in PNAS revealed that E. coli bacteria can be used to produce biodiesel that is identical to the fossil fuel diesel that we currently use. This work has been pioneered by Dr. John Love. He's from Exeter University. John, why were you trying to do this? What was the motivation?
John - The original motivation was that, the current biofuels that we use in the first generation, ethanol and plant-derived biodiesel are actually not that good. Not just because of the problems that you were mentioning earlier but also because basically, in a car engine, they're not great, they don't burn very well. They have problems that clog up the engine, there are issues with quality control as well. And so really, what we wanted to do was to see if we can generate biologically, a fuel that was exactly what we needed for the retail fuel market. And rather than actually sort of having substitutes or additives, what we can do is have fuel replacements that wouldn't affect the efficiency of modern engines.
Chris - I was of the opinion that scientists are already modifying microorganisms to produce diesel and diesel-like substitutes - algae for example. So, what can you add by doing it in E. coli instead?
John - So basically, algae are very, very useful actually and I also do work a little bit on algae and I'm a big fan of algae. The problem is, is that the amount of land required to actually grow algae right now is substantial and also, the amount of capital expenditure into developing algal farms is very, very large right now. Even though you've got the concept of the integrated bio-refineries whereby you could use water treatment plants to feed algae and maybe nuclear power, hot water to actually heat them up, there are some issues regarding algae which you just can't get around and that is the amount of sun hitting the pond and the depth of pond, self-shading, and all these sort of issues.
Chris - And of course, E. coli will grow in the dark so you can get around that problem.
John - It will grow in the dark, it will grow in a great big tower so essentially, your land footprints are quite low and also the technologies of E. coli fermentation if you like are there in the pharmaceutical industry and the technologies of say, the brewing industry which relies on yeast can be fitted into an E. coli-style system.
Chris - So first off, what does it take to make E. coli make diesel because just in case anyone isn't aware of this, E. coli don't make diesel normally do they?
John - No, they don't, not at all. In fact, it's quite intriguing because a lot of microorganisms do make a lot of alkane-like compounds. A lot of animals actually make alkane-like compounds. For instance, birds use an alkane-like wax to waterproof their feathers. Plants use it on their cuticles to stop water evaporating from their leaves. Insects use it in their cuticles for the same reason. Cyanobacteria use it as well for a reason that we don't really understand just yet. But the thing is that E. coli does not do it. E. coli was a work horse of the laboratory and so, what we felt we'd do is, if we cannot find the organisms that can make the alkanes in sufficient amounts, can't we engineer them to make the alkanes that we need and that we want? So, what we did is we trawled the literature, trawled the gene bank and various things like that, came up with a few solutions that were possible and then built artificial synthetic metabolic pathways in order to generate the biofuels. And the conversion basically goes from free fatty acids to an aldehyde to the alkane. And we trim and we customise the chain length, the carbon chain length and the carbon chain configuration at the free fatty acid stage.
Chris - So in other words, what you feed the bugs determines what they churn out.
John - Well, not really, no, because actually, what we feed the bugs right now is glucose and really, glucose is a source of most of the energy in the E. coli cell and it will eventually be converted to a free fatty acid. If we were able to feed it another substrate, then it would just use it as an energy source and it would also take that to a free fatty acid, providing there's some carbon there, we can actually construct these fatty acid carbon chains.
Chris - So, you've taken chunks or modules of, I suppose, bits of metabolic pathways from a range of different microorganisms, reassemble them all in E. coli so it's got this ability to do this synthesis, it then makes these chemicals that to all intents and purposes are very similar in composition to diesel. How much can I get from one bacterium or if I grow a culture of them, can you get practical amounts out?
John - Well, right now, no, you can't and so, what we've done essentially, the proof of principle. What we need to do next is to actually work out the bottle necks in the metabolic pathways to try and iron out any competing reactions to make the process much more efficient, and potentially, also boost the amount of fatty acid that is produced by E. coli. And there's a wide literature in actually doing that. So, that might be relatively feasible. What we'd also like to do is alter the inputs if you like into the system, not just the outputs so that we can get the E. coli to feed off a variety of substrates and not just right now, glucose, but perhaps sugars derived from lignocellulose, so the degradation of wood or perhaps even waste products, we accept as useful right now.