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A team of researchers from the Massachusetts Institute of Technology (MIT) has shown that single-celled microorganisms like Escherichia coli and Saccharomyces cerevisiae that do not normally inhabit hydrogen-rich environments can survive and grow in a 100% hydrogen atmosphere.
Next-generation telescopes could first search for hydrogen-dominated exoplanet atmospheres, since hydrogen can be a viable and easily detectable biosignature of life. Image credit: Sci-News.com.
“There are a diversity of habitable worlds, and we have confirmed that Earth-based life can survive in hydrogen-rich atmospheres,” said Dr. Sara Seager, a researcher with the Department of Earth, Atmospheric and Planetary, and Science, Department of Physics. and MIT’s Aeronautics and Astronautics Department.
“We should definitely add those kinds of planets to the options menu when thinking about life on other worlds, and actually try to find it.”
On primitive Earth billions of years ago, the atmosphere looked very different from the air we breathe today. The infant planet still lacked oxygen, and was made up of a gas soup, which included carbon dioxide, methane, and a very small fraction of hydrogen.
Hydrogen gas remained in the atmosphere for possibly billions of years, until what is known as the Great Oxidation Event, and the gradual accumulation of oxygen.
The small amount of hydrogen that remains today is consumed by certain ancient lines of microorganisms, including methanogens, organisms that live in extreme climates, such as deep in the ice, or within the desert floor, and gobble up hydrogen, along with carbon dioxide, to produce methane. .
Scientists routinely study the activity of methanogens grown in laboratory conditions with 80% hydrogen. But there are very few studies exploring the tolerance of other microbes to hydrogen-rich environments.
“We wanted to demonstrate that life survives and can grow in a hydrogen atmosphere,” explained Dr. Seager.
Dr. Seager and his colleagues studied the viability of two types of microbes: the bacteria Escherichia coli, a simple prokaryote and the yeast SAccharomyces cerevisiae, a more complex eukaryote, in a 100% hydrogen environment.
In their experiments, they separately cultivated yeast cultures and Escherichia coliHe then injected the cultures with the microbes into separate bottles, filled with a broth, or a nutrient-rich culture that the microbes could feed.
They then expelled the oxygen-rich air in the bottles and filled the remaining headspace with a certain gas of interest, such as a 100% hydrogen gas.
They then placed the bottles in an incubator, where they were gently and continuously shaken to promote mixing between microbes and nutrients.
Every hour, they collected samples from each bottle and counted the live microbes. They continued taking samples for up to 80 hours.
Their results represented a classic growth curve: at the beginning of the test, the microbes grew rapidly in number, feeding on the nutrients and populating the crop. Finally, the amount of microbes stabilized. The still prosperous population remained stable as new microbes continued to grow, replacing those that died.
“We did not find surprising results. After all, hydrogen is an inert gas, and as such is not inherently toxic to organisms, ”said Dr. Seager.
“It is not as if we have filled the upper space with a poison. But seeing is believing, right? If no one has studied them, especially eukaryotes, in an environment dominated by hydrogen, they will want to do the experiment to believe it.”
“The experiment was not designed to show whether microbes can depend on hydrogen as an energy source. Rather, the point was more to demonstrate that a 100% hydrogen atmosphere would not harm or kill certain life forms. ”
“I don’t think it has occurred to astronomers that there might be life in a hydrogen environment. I hope the study encourages cross-talk between astronomers and biologists, particularly as the search for habitable planets and extraterrestrial life increases.”
The findings were published in the journal. Astronomy of nature.
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S. Seager et al. Laboratory studies on the viability of life in H2exoplanet atmospheres dominated. Nat astron, published online May 4, 2020; doi: 10.1038 / s41550-020-1069-4
