Hydrothermal vents source of first cell membrane material

The origin of life on Earth - and beyond - is a mystery, and, arguably, one of the most important questions to answer. We know that life started simply, probably with self-replicating chemical reactions most likely based around something similar to the DNA molecules we rely on to carry our genetic code today. But, pretty quickly, those reactions found a way to wrap themselves up inside oily membranes that could protect them from the surroundings and make the process more reliable and efficient. Hey presto, the cell was born. But where did those membranes, made of fatty acids, come from in the first place? That question has bothered biologists for decades. Now, though, researchers at Newcastle University have recreated in the lab the conditions around hydrothermal vents, also known as underwater black smokers. These conditions, Jon Telling has found, can spontaneously generate the very molecules that scientists have been searching for…

Jon - There's a few lines of evidence that point towards these hydrothermal vents, these hot springs, as a likely place for where life originated. People have tried to find out what the earliest cell that everything originates from was like, and what they've deduced from looking at the genes is that the first cell - known as the 'last universal common ancestor' - liked it hot, it probably lived off hydrogen gas, and it would've used carbon dioxide as well to build itself. So those lines of evidence all point towards these hot springs as a possible place for the origin of life.

Chris - It sounds like we actually know quite a bit in terms of what we expect that ancestor to have been like. But what was the outstanding question you were trying to crack with relation to it, then?

Jon - Previous people have tried running different experiments to try and mimic some of the conditions that these hydrothermal vents would've had. People had either tried to recreate, say, the high temperatures or the high pressure, or the kind of continuous flow where you're mixing seawater with this hotter fluid, but nobody had really gone on trying to combine all of those at once. That's what we wanted to do. We built some new apparatus in our lab to try and get that; the high pressure, get the high temperature, and get the continuous flow all in one experiment and try and react this hydrogen gas and this carbon dioxide over these metals to see if we could generate organic molecules.

Chris - What source of molecules were you looking for?

Jon - Ones we were particularly interested in were these molecules known as fatty acids. They have a fatty end and a water loving end. The interesting thing about them is, if you get enough of them in that water, then they can form what are known as these membrane structures, vesicles or liposome sometimes they're known as, but they basically form these little round balls surrounded by a membrane which separates what's in them from what's outside. So it is acting in a way as a sort of first cell membrane, potentially, which could separate the external environment from the internal and let different chemistry happen.

Chris - I understand where you're going with that because obviously that was the big question, wasn't it? If life gets started as a series of chemical reactions, where did cells come from? So if you've got a reaction that can produce the oily bags that surround all our cells, that is 90% of the equation.

Jon - Well, it's certainly a good step forward. It's the first step to creating a self, something different from what's outside. The ability to do that and then concentrate chemicals differently to outside, generate different reactions, would've been I think an essential step for how life started.

Chris - What are the raw materials that you are feeding into your pretend hydrothermal vent and what chemicals did you see coming out at the end in these conditions that lead you to think that is possibly how some primitive cell like structures could have formed?

Jon - What we fed in, the basis of it was hydrogen gas which we added under pressure. Then, we combined that with dissolved carbon dioxide. We're reacting them over a mineral, in this case an iron rich mineral known as magnetite, to form hydrocarbons: organic molecules. In particular we were looking for these fatty acid molecules, which are a type of hydrocarbon.

Chris - And do you get many and how quickly?

Jon - The experiments we've run so far, we only ran for 16 hours and in that time, yeah, we generated enough to find them. If we run it for longer, we might find that we generate even more of them, but there are certainly enough of these organic molecules for us to analyse.

Chris - Do they start to self assemble? Because the point you're making is that the fatty bits love other fatty bits, so they tend to get together. So do you start to see that happening?

Jon - As yet, no, because when they form they actually form on the mineral surface. The next stage of experiments that we want to do is to try and do this: to actually change the chemical conditions. We think there may be, if we make the environment more alkaline, we can get some of these molecules, particularly these fatty acids, to lift off and hopefully we could then see them self-assemble.

Chris - If we bring what you found to the party that already people had envisaged as to how life could have got started, how do you bring and unite your discovery of how these fatty acids begin to form with what people thought might also be going on around the same time, about 4 billion years ago, that was the start of life?

Jon - People have found these reactions going on at higher temperatures, for example, before. What we've done is do these experiments under more realistic conditions as to what the conditions may have been like on the early Earth. And it just gives that greater likelihood, I think, that these really important organic molecules may well have been formed within these sub ocean hydrothermal vents. And it might also increase our understanding as well, I think, about how life may have originated in other places in our solar system, or whether a similar chemistry might be going on.

Chris - I was going to ask you about that because of course we've got missions that are going to be looking at Europa, which is one of Jupiter's moons. People have also considered Enceladus, one of Saturn's moons, which appear to have warm liquid oceans beneath the surface of ice. So it's possible the conditions there might be similar to the conditions you are mimicking in your laboratory?

Jon - Exactly. I think the best characterised ocean so far is actually Saturn's moon Enceladus. There's actually a spacecraft which has travelled around, known as Cassini, and it's actually sampled these plumes which people think are emanating from beneath the icy layer of Enceladus into this ocean. So you've got part of this ocean actually being blasted out into space and been analysed, and when they've analysed the vapours and particles that are in this plume, they found hydrogen gas, they found carbonates - so signs that carbon dioxide there as well. And they've also analysed different organic molecules. It seems that all the ingredients, potentially, for an origin of life might be there, but it's going to take a fair few more experiments to try and narrow that down further.