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Amazing news about the origin of life.

Minerals near deep-sea hydrothermal vents

promote the formation of energy-rich organic

molecules that life needed to get its start.

Was this life's first meal?

By Robert F. ServiceMar. 2, 2020 , 12:30 PM

Studies of the origin of life are replete with

paradoxes.

Take this doozy: Every known organism on

Earth uses a suite of proteins-and the DNA

that helps build it-to construct the building

blocks of our cells.

But those very building blocks are also needed

to make DNA and proteins.

The solution to this chicken-and-egg conundrum

may lie at the site of hydrothermal vents, fissures

in the sea floor that spew hot water and a wealth

of other chemicals, researchers report today.

Scientists say they have found that a trio of metal

compounds abundant around the vents can cause

hydrogen gas and carbon dioxide (CO2) to react

to form a collection of energy-rich organic

compounds critical to cell growth.

And the high temperatures and pressures around

the vents themselves may have jump-started life

on Earth, the team argues.

The new work is "thrilling," says Thomas Carell,

an origin of life chemist at Ludwig Maximilian

University of Munich who was not affiliated with

the new project.

The organic molecules the study generated

include formate, acetate, and pyruvate, which

Carell calls "the most fundamental molecules

of energy metabolism," the process of converting

nutrients into cell growth.

The new results support a long-held idea about

the origin of life known as "metabolism first

hypothesis.

" It posits that geochemical processes on early

 Earth created a stew of simple energy-rich

compounds that drove the synthesis of complex

molecules, which eventually provided the

materials for Darwinian evolution and life.

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A clue to this primordial metabolism came in 2016.

Researchers led by William Martin, an evolutionary

biologist at Heinrich Heine University of Dusseldorf,

scanned the genomes of thousands of bacteria and

archaea, identifying 355 proteins encoded by shared

genes that likely belonged to a microbial Eve, the

last universal common ancestor of all life.

Those proteins suggest this primordial microbe

thrived in scalding temperatures and ate hydrogen

gas, using its electrons to convert inorganic CO2

 dissolved in the ocean into energy-rich organic

compounds.

That supports the notion that the microbes lived

near hydrothermal vents, where those conditions

would have been present.

That idea is bolstered by the fact that modern

organisms still combine hydrogen and CO2 to

make organic molecules in a process known

as the acetyl-coenzyme A (acetyl-CoA) pathway.

This process feeds essential organic molecules

into biochemical processes that drive the

production of proteins, carbohydrates, and lipids,

which is at the heart of energy metabolism in cells.

The problem, however, is that modern organisms

run the acetyl-CoA pathway using 11 enzymes

made up of a combined 15,000 amino acids, all

finely positioned to carry out their work.

And without the right protein machinery or catalyst,

if you put hydrogen and CO2 together, Martin says,

"Nothing will happen."

So how could organisms have spontaneously

developed their prowess to run the acetyl-CoA

pathway? Two years ago, researchers led by Joseph

Moran, a chemist at the University of Strasbourg,

suggested at least a partial answer.

They reported that pure metals, including iron,

nickel, and cobalt, could catalyze the reaction of

water (water molecules contain hydrogen) and

CO2 to form acetate and pyruvate, key members

of the acetyl-CoA pathway.

That finding suggests the earliest life could have

simply fed on these organic compounds to get

a toehold, and over time evolved a suite of proteins

to make the reactions even more efficient.

Still, Martin notes, converting water and CO2 into

needed organics isn't how microbial Eve's most

closely related modern brethren do it.

Rather, these organisms start with hydrogen gas

and CO2. "We wanted to see if we could get this

pathway to work without enzymes," Martin says.

He and his colleagues knew hydrothermal vents

continually spew out hydrogen gas, driven by

reactions between water and metals deep below

Earth's crust.

And researchers previously determined that CO2

 in early Earth's oceans was about 1000 times

more abundant than it is today.

So, Martin wondered whether metal-rich minerals

common around hydrothermal vents could cause

hydrogen to react with CO2.

To find out, Martin's and Moran's teams joined

forces to investigate three iron-rich minerals found

near vents: greigite, magnetite, and awaruite.

They added these to a water solution and bubbled

in hydrogen and CO2 at 100°C and 25 bars of

pressure, conditions common around deep-sea

vents.

All three minerals catalyzed a reaction of hydrogen

and CO2 to form a mix of organics including formate,

acetate, and pyruvate, the group reports today

in Nature Ecology & Evolution.

"What we have here is a sustained source of

chemical energy, and it generates these energy-

rich molecules used in metabolism," Martin says.

So, was this mix of organics life's first meal? It's

a fair bet, says Steven Benner, a chemist at the

Foundation for Applied Molecular Evolution.

For evolution to begin, life would have needed both

a food source and some form of protogenetic

molecule to transmit information from one organism

to its progeny.

How they came together is still unclear.

However, any early Darwinian system would need

to feed.

And, Benner says: "The process described by

[Martin's and Moran's team] could certainly h

ave been the source of some of their food."

Posted in: 

• Chemistry
• Earth

doi:10.1126/science.abb5418

Robert F. Service

Bob is a news reporter for Science in Portland,

Oregon, covering chemistry, materials science,

and energy stories.