As two bio-geoscientists, Jeffrey Dick and Everett Shock have discovered that some hydrothermal seabed settings offer a unique home for particular organisms. This has opened up new possibilities for life in deep waters on Earth and across the solar system; Cellular respiration is the mechanism by which organisms get energy from the food they consume on land by ingesting oxygen and exhaling carbon dioxide. The chemicals in our food are biologically unstable in the presence of oxygen: this instability that our cells use to grow and reproduce, a process known as biosynthesis. Journal of Geophysical Research: Biogeosciences has published their findings.
However, the circumstances for life on the seabed are vastly different. Co-author Shock of Arizona State University's School of Earth and Space Exploration and the School of Molecular Sciences remarked, "On land, in the oxygen-rich atmosphere of Earth, it is known to many people that building molecules of life take energy."
"It's a startling contrast, though, when heated fluids meet with cold saltwater near hydrothermal vents, creating a unique environment in which the formation of molecules of life releases energy."
Vents in deep-sea microbial communities are where organisms flourish because hydrothermal fluid and seawater interact. It was previously shown that the biosynthesis of fundamental cellular building blocks, such as amino acids and glucose, is more beneficial in places where the vents are composed of ultramafic rock (igneous and meta-mafic rocks with low silica concentration). Polymers, also known as biomacromolecules, are bigger molecules that organisms must synthesize from the fundamental building blocks of amino acids and carbohydrates. The polymerization process (where tiny molecules unite to make a bigger biomolecule) needs energy in practically all imaginable situations, and proteins are the most numerous of these molecules in cells.
Lead author Dick explains that "in other words, when there is life and water, polymerization is advantageous, but water must be removed from the system for this to occur." He is presently a geochemistry researcher at China's Central South University, where he is currently a postdoctoral fellow.
"There are two competing energy flows energy released by fundamental building block biogenesis and energy needed for polymerization."
Dick and Shock wanted to discover whether the total synthesis of proteins in the mixing zone is beneficial when you add them all together. They used a novel mix of theory and data to approach this challenge.
"Group additivity," a thermodynamic model for proteins, was employed to account for the individual amino acids in protein sequences and polymerization energies from the theoretical perspective. They used the whole genome of Methanocaldococcus jannaschii, a well-studied vent bacterium, for their findings.
This organism develops quickest at a temperature of around 185 degrees Fahrenheit where practically all of its proteins are synthesized, according to the calculations they made (85 Celsius). While in a basalt-hosted environment, where hydrogen production is lower, the synthesis of proteins is more complicated.
For the first time, researchers have discovered that specific organisms are more likely to thrive in particular hydrothermal settings, according to Dick.
It has been observed that methanogens, such as Methanocaldococcus jannaschii, are more prevalent in ultramafic-hosted vent systems than in basalt-hosted systems. That distribution is consistent with the favorable energetics of protein production in ultramafic-hosted systems. If these estimates can be applied throughout the tree of life, scientists expect to offer a more solid relationship between geochemistry and genome evolution.
"We're reminded time and time again as we investigate that where we live should never be equated with what is hospitable to life," Shock added.
Dick, J. M., & Shock, E. L. (2021). The release of energy during protein synthesis at ultramafic-hosted submarine hydrothermal ecosystems. Journal of Geophysical Research: Biogeosciences, 126, e2021JG006436. https://doi.org/10.1029/2021JG006436