Life arose on hydrogen energy, researchers suggest

Date:
December 13, 2021
Source:
Heinrich-Heine University Duesseldorf
Summary:
How did the first chemical reactions get started at the origin
of life and what was their source of energy? Researchers have
reconstructed the metabolism of the last universal common ancestor,
LUCA. They found that almost all chemical steps used by primordial
life to piece together the molecular building blocks of cells
are energy releasing reactions. This identified the long-sought
source of energy needed to drive these reactions forward, which
has been hiding in plain sight. The energy required to synthesize
the building blocks of life comes from within metabolism itself,
as long as one essential starting compound is included. The secret
ingredient that releases the energy from within at life's origin is
the cleanest, greenest, newest and oldest of all energy carriers:
Hydrogen gas, H2.



FULL STORY ==========================================================================
How did the first chemical reactions get started at the origin of life
and what was their source of energy? Researchers at the Heinrich Heine University Du"sseldorf (HHU) have reconstructed the metabolism of the
last universal common ancestor, LUCA. They found that almost all chemical
steps used by primordial life to piece together the molecular building
blocks of cells are energy releasing reactions. This identified the
long-sought source of energy needed to drive these reactions forward,
which has been hiding in plain sight.

The energy required to synthesize the building blocks of life comes from
within metabolism itself, as long as one essential starting compound is included. The secret ingredient that releases the energy from within at
life's origin is the cleanest, greenest, newest and oldest of all energy carriers: Hydrogen gas, H2.


==========================================================================
The team of Prof. Dr. William Martin in the Institute for Molecular
Evolution at the HHU investigates how and where life arose on the
early Earth. Their approach is experimental and computational. In the laboratory, they run chemical experiments to investigate reactions between hydrogen and carbon dioxide, CO2, using catalysts and conditions found
in submarine hydrothermal vents. At the computer, they have developed
a form of molecular archaeology that allows them to uncover the many
different traces of primordial life that are preserved in the proteins,
DNA and chemical reactions of modern cells.

In their latest work, they investigated the question of what kind of
chemical environment fostered the chemical reactions that gave rise to metabolism, and later to LUCA itself, and where the energy came from that
was needed to drive those reactions forward. To do that, they looked
not at genes, but at the information contained within the chemical
reactions of life themselves. They identified 402 metabolic reactions
that have gone virtually unchanged since the origin of life roughly
4 billion years ago. Because these reactions are common to all cells,
they were also present in LUCA. They shed light on how primordial life
dealt with energy in metabolism and where it obtained the energy needed
to make life's chemical reactions go forward.

Jessica Wimmer, a PhD student in the institute and lead author on the
new paper, was particularly interested in the energy balance of LUCA's metabolic reactions, because all life requires energy. For that she
made a catalogue of the 402 reactions that the simple and ancient
among modern cells -- bacteria and archaea -- use to construct the
building blocks of life: the 20 amino acids, the bases of DNA and RNA,
and the 18 vitamins (cofactors) that are essential for metabolism. In
the most primitive of modern cells, and in Wimmer's computer analyses,
these compounds are synthesized from simple molecules that are present
in the modern environment and that were also present in hydrothermal
vents on the early Earth: hydrogen (H2), carbon dioxide (CO2) and ammonia (NH3). The result was the metabolic network of LUCA.

When asked about the motivation behind the central question of the new
study, Jessica Wimmer says: "We wanted to know where the energy came from
that drove primordial metabolism forward. At the very onset of metabolic reactions some 4 billion years ago, there were no proteins or enzymes
to catalyze reactions because they had not yet evolved. Metabolism
had to arise from reactions that could take place in the environment,
perhaps with help from inorganic catalysts. But catalysts or not, in
order to go forward, the reactions have to release energy. Where did
that energy come from? There have been lots of suggestions for possible
sources of metabolic energy in the literature. But nobody ever looked
into the reactions of metabolism itself." To find sources of energy
in metabolic reactions, the team calculated the amount of free energy,
also called Gibbs energy, that is released or consumed in each reaction.

The result: LUCA's metabolism required no external source of energy such
as UV light, meteorite impacts, volcanic eruptions, or radioactivity. On
the contrary, in an environment typical of many modern submarine
hydrothermal vents, the energy needed for the reactions of metabolism to
go forward stems from within metabolism itself. Stated another way, almost
all of LUCA's metabolic reactions liberate energy all by themselves:
the energy for life stems from life itself. Martin, senior author of the
study, says: "That is exciting, because the 400 interconnected reactions
of central metabolism, which seem so hopelessly complex upon first
encounter, suddenly reveal a natural tendency to unfold all by themselves
under the right conditions." To arrive at that conclusion, the team had
to first investigate the energetics of the 402 reactions using computer programs that simulate different environmental conditions, so as to
distinguish energetically favorable from unfavorable combinations. This
is important because whether or not a reaction releases energy often
depends upon environmental conditions. They surveyed conditions ranging
from pH 1 (acidic) to pH 14 (alkaline), temperatures from 25 to 100
DEGC, and different relative amounts of reactants to products. They
looked with particular care at the energetic role of hydrogen. Wimmer:
"Without hydrogen, nothing happens at all, because hydrogen is required
to get carbon from CO2 incorporated into metabolism in the first place."
The energetically optimal conditions fall within an alkaline pH range
around pH 9 and a temperature around 80 DEGC, with hydrogen required
for CO2 fixation.

Putting this result in context, Martin explains: "This is almost
exactly what we see at Lost City, a H2-producing hydrothermal field in
the Mid-Atlantic. In an environment like that, about 95-97 % of LUCA's metabolic reactions could go forward spontaneously, that is, without
the need for any other source of energy. In the abyssal darkness of hydrothermal systems, H2 is chemical sunlight. Modern energy research
exploits exactly the same properties of hydrogen as life does. It
is just that life has four billion years of experience with hydrogen technology, while we are just getting started." Jessica Wimmer adds: "Regarding energy at life's origin, we can say that pure chemical energy
is sufficient. We need no sunlight, no meteorites, no UV light: just
H2 and CO2, plus some ammonia and salts. Because of the extremely
conserved nature of the chemical reactions in our biosynthetic
network, we can obtain some interesting insights into the reactions
that gave rise to LUCA, even though it lived four billion years ago." ========================================================================== Story Source: Materials provided by
Heinrich-Heine_University_Duesseldorf. Original written by Arne
Claussen. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jessica L. E. Wimmer, Joana C. Xavier, Andrey d. N. Vieira,
Delfina P. H.

Pereira, Jacqueline Leidner, Filipa L. Sousa, Karl Kleinermanns,
Martina Preiner, William F. Martin. Energy at Origins: Favorable
Thermodynamics of Biosynthetic Reactions in the Last Universal
Common Ancestor (LUCA).

Frontiers in Microbiology, 2021; 12 DOI: 10.3389/fmicb.2021.793664 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211213084117.htm

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