New possibilities for life on Earth’s seabed and beyond


Two biogeoscientists have opened up new possibilities for life in the dark at the bottom of Earth’s oceans, as well as in the entire solar system.

At Journal of Geophysical Research: Biogeosciences, Jeffrey Dick, and Everett Shock have determined that specific hydrothermal seafloor environments provide a unique habitat where certain organisms can thrive.

In the strange and dark world of the ocean floor, underwater fissures, called hydrothermal vents, are home to complex communities of life.. These vents spew scorching hot fluids into extremely cold seawater, creating the chemical forces necessary for the tiny organisms that inhabit this extreme environment to live.

On land, when organisms obtain energy from the food they eat, they do so through a process called cellular respiration. where there is an intake of oxygen and the release of carbon dioxide. Biologically speaking, the molecules in our food are unstable in the presence of oxygen, and it is this instability that our cells take advantage of to grow and reproduce, a process called biosynthesis.

But for organisms that live on the seafloor, the living conditions are dramatically different.

“On land, in Earth’s oxygen-rich atmosphere, many people are familiar that making the molecules of life requires energy,” he said. it’s a statement co-author Shock from the School of Earth and Space Exploration and the School of Molecular Sciences at Arizona State University. “In astonishing contrast, around hydrothermal vents on the seabed, hot fluids mix with extremely cold seawater to produce conditions in which the molecules of life release energy. “

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In deep-sea microbial ecosystems, organisms thrive near vents where hydrothermal fluid mixes with ambient seawater. Previous research led by Shock found that the biosynthesis of basic cellular building blocks, such as amino acids and sugars, is particularly favorable in areas where the vents are composed of ultramafic rock (igneous and meta-igneous rocks with very low silica content), because these rocks produce the most hydrogen.

In addition to building blocks like amino acids and sugars, cells need to form larger molecules or polymers, also known as biomacromolecules. Proteins are the most abundant of these molecules in cells, and the polymerization reaction (where small molecules combine to produce a larger biomolecule) it requires power in almost every environment imaginable.

In other words, where there is life, there is water, but the water must be flushed out of the system for polymerization to be favorable.“said lead author Dick, who was a postdoctoral fellow at Arizona State when this research began and is currently a geochemistry researcher at the School of Geosciences and Info-Physics at Central South University in Changsha, China.” So there is two opposing energy flows: the release of energy by biosynthesis of basic building blocks and the energy required for polymerization. “

What Dick and Shock wanted to know is what happens when you add them up: do you get proteins whose overall synthesis is really favorable in the mixing zone? They tackled this problem using a unique combination of theory and data.

Theoretically, they used a thermodynamic model for proteins, called “group additivity,” which explains the specific amino acids in protein sequences, as well as the polymerization energies. For the data, used all the protein sequences in a complete genome from a well-studied vent organism called Methanocaldococcus jannaschii.

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By running the calculations, they were able to show that the general synthesis of almost all proteins in the genome releases energy into the mixing zone of a vent housed in ultramafics at the temperature where this organism grows the fastest, around 85 degrees Celsius.) In contrast, in a different ventilation system that produces less hydrogen (a basalt-housed system), protein synthesis is not favorable.

“This finding provides a new perspective not only on biochemistry but also on ecology because it suggests that certain groups of organisms are inherently more favored in specific hydrothermal environments“said Dick.” Microbial ecology studies have found that methanogens, of which Methanocaldococcus jannaschii is representative, are more abundant in ultramafic-housed ventilation systems than in basalt-housed systems. The favorable energy of protein synthesis in ultramafic-housed systems is consistent with this distribution. “

For the next steps, Dick and Shock are looking for ways to use these energetic calculations in the tree of life, They hope will provide a stronger link between geochemistry and genome evolution.

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