The first living organisms may have relied on nickel and sulphur to obtain energy and sustain themselves. That is the conclusion of a study that shows how nickel sulphide can transform simple chemicals into many of the substances that underpin life. It is one of several recent studies indicating that life-like processes can be kick-started by metals.
鈥淲e are able to build up important biomolecules from simple precursors,鈥� says Claudia Huber at the Technical University of Munich in Germany.
Huber and her colleagues have spent over 20 years investigating how life started. They focus on the origin of metabolism聽鈥� the that organisms use to obtain energy and build their bodies.
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Modern organisms such as plants convert carbon dioxide into sugars 鈥� technically called 鈥渇ixing鈥� carbon 鈥� by carrying out intricate cycles of chemical reactions. These reactions are controlled by complicated molecules called enzymes, which cannot have existed when life started. So Huber鈥檚 team has studied whether other, simpler chemicals can make the reactions work. The team鈥檚 work was prompted by the ideas of G眉nter W盲chtersh盲user, a Munich patent lawyer .
The researchers began with two carbon-based chemicals: carbon monoxide and acetylene. Both are thought to have been present when Earth was young. They mixed them with nickel sulphide, a common mineral, and heated them to 105掳C 鈥� the sort of temperature seen in water heated by volcanic rocks.
The result was a smorgasbord of carbon-based chemicals, including acetate, pyruvate and succinate. These chemicals are found in the metabolic processes used by all microorganisms, says Huber.
It doesn鈥檛 stop there. 鈥淥ur products undergo further reactions in the same system,鈥� mimicking those that take place in living cells, says Huber. She thinks that the kind of carbon fixing reactions we see in plants and bacteria today could have evolved from these systems.
In a 2016 study, Huber鈥檚 team showed that , which could have formed the outer membranes of the first cells.
Primordial metabolism
鈥淚t鈥檚 well supported,鈥� says Joseph Moran at the University of Strasbourg in France. 鈥淭hey鈥檝e been thinking about the connections to carbon fixation chemistry, which I think is a good thing to think about.鈥�
However, Moran isn鈥檛 convinced that acetylene and carbon monoxide are the most likely starting points. 鈥淓veryone agrees carbon dioxide would be present on the early Earth and we know that鈥檚 how life gets its carbon today, so that would be the ideal feedstock,鈥� he says.
The issue is that carbon dioxide is fairly unreactive, so minerals like nickel sulphide don鈥檛 give enough of a chemical push . Huber鈥檚 team avoided this problem by replacing carbon dioxide with the more reactive acetylene and carbon monoxide.
However, in his own research Moran has used carbon dioxide, instead mixing it with more potent drivers. 鈥淚n our work we use metallic iron,鈥� he says. 鈥淚t鈥檚 80 per cent of the core of the Earth, and it鈥檚 in meteorites.鈥�
In a , Moran鈥檚 team has shown that found in many metabolic processes, and , without the need for enzymes.
Huber says Moran and his colleagues are doing valuable research into the earliest metabolism 鈥� particularly since it also focuses on the importance of fixing carbon.
鈥淚鈥檓 very hopeful that there鈥檒l be, in short order, non-enzymatic versions of all the metabolic pathways,鈥� says Moran.
Life
