Here is our latest paper about protocell formation at the origin of life in alkaline hydrothermal vents. You can also check out my “Behind the Paper” piece below.
Month: November 2019
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Protocells in deep sea hydrothermal vents: another piece of the origin of life puzzle
The following is a piece I wrote for the Nature Ecology and Evolution community “Behind the Paper” series. See the original here.
An origin of life in deep sea hydrothermal vents has been deemed problematic due to the inability to form lipid vesicles in saline solutions. Our latest research suggests this may not be as difficult as we once thought.
![An alkaline hydrothermal vent An alkaline hydrothermal vent](https://natureecoevocommunity.nature.com/cdn-cgi/image/quality=45/https://s3.amazonaws.com/zapnito/uploads/d291058e7cf6368b33fb8796be7c6266/e39d59e4-7dbb-4b41-96e3-b7d4bb89bf6d.jpeg)
An alkaline vent at the Lost City hydrothermal field
We noticed that one common theme of these experiments was that they all used a combination of 1-3 SCAs to form vesicles. This seemed at odds with the Fischer-Tropsch-type synthesis which can produce up to around 40 different SCAs, with the most abundant chain lengths in the region of 10-15 carbon atoms, under hydrothermal conditions. So we decided to try using slightly more complex mixtures of SCAs whilst keeping the molecules themselves very simple. This is arguably more representative of the actual conditions on the early Earth. In our recent Nature Ecology and Evolution paper we show that using mixtures of 12 fatty acids and alcohols at low concentrations under alkaline hydrothermal vent-like conditions (i.e. 70 °C and pH ~12) we were able to form vesicles in sea water concentrations of sodium chloride, magnesium, or calcium. Straight away we had observed the benefits of increasing the number of SCAs in a mix. Unfortunately, in a solution containing all these salts together, vesicles became aggregated. Around this time we had been discussing the idea of isoprenoids at the origin of life. These form the tails of archaeal phospholipids, the position taken by fatty acids in bacterial phospholipids. Phylogenetics suggests that the last universal common ancestor (LUCA) had the capability to synthesise both of these lipid types. It is possible then that isoprenoid acids and alcohols could have played a role in membrane formation at the origin of life, yet very little work has been done on vesicle formation with isoprenoids. So we added geranic acid and geraniol, both C10 isoprenoid molecules, to our 12 SCA mixture. These 14 component vesicles formed readily in the most extreme hydrothermal mixtures of salts and were stable enough to encapsulate fluorescent dyes over 24 hours.
Confocal microscope image of mixed SCA vesicles in alkaline fluid.
They key point here is that vesicles can and do form in oceanic conditions. For the mixtures we used the alkaline vent conditions were actually essential. Below temperatures of about 60-70 °C or pH 11-12 vesicles did not form – but once formed under these conditions they can persist at lower temperatures and pH. However, there are myriad SCAs simple enough to have been available for vesicle formation at the origin of life. It is likely that with continuing research we will find combinations that could provide bilayer membranes in almost any environment. The idea that vesicle formation from simple SCA mixtures should lead researchers to cast aside a theory for the origin of life is clearly unreasonable. We hope that this work will encourage others to increase the complexity of mixtures of various prebiotically plausible molecules to expand our understanding of how the first protocells might have formed and behaved at the origin of life.
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The origin of life: the submarine alkaline vent theory at 30
The Lane Lab contributed two research articles to this issue including one in which I was the lead author. This paper is the culmination of some really interesting discussions between Nick and myself followed by some long hours in the lab trying to follow up on our ideas. We shed some light on the potential for protocell membranes to contain both fatty acids and isoprenoids, possible precursors to bacterial and archaeal membrane lipids respectively. We look at the some of the possible pros and cons of this and how these may have contributed to an early lipid divide! There is a lot more to do on this topic and hopefully this will be the first of several publications probing this aspect of protocell membranes more deeply.
See the whole issue here, check out the protocell paper here, and read our paper on CO2 reduction here!