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Wednesday, October 21, 2020
In May, a study conducted by Massachusetts Institute of Technology professor Dr Sara Seager and other researchers showed single-celled organisms like Escherichia coli and yeast can thrive in both 100% hydrogen gas and helium atmospheres. Wikinews discussed the findings with Dr Seager to know more about her research.
Life has not been observed to habitat other than Earth which has oxygen-rich environment. While Earth’s atmosphere is dominated by nitrogen-gas, oxygen is essential for most of the living organisms. There are few species of microorganisms which do not require oxygen for metabolism, referred as anærobic organisms. However, many anærobics rely on methane or nitrogen in order to thrive. Methane and nitrogen are not nearly as abundant as hydrogen and helium in the universe. Detection and study of exoplanets with hydrogen or helium atmosphere is easier as compared to nitrogen or carbon dioxide-rich atmosphere.
Researchers used Escherichia coli strain K-12 and Saccharomyces cerevisiæ strain S288C for this experiment.The two microorganisms were kept in four different environments: one being 100% air, and other three being anærobic environments: 100% H2, 100% He, and 80%-20% N2-CO2. The environments were kept in at 28°Celsius. The researchers made sure experiment environment was anoxic, and had installed oxygen sensors to report fluctuation in the oxygen level. They monitored growth of E. coli using optical density measurement, and they used hæmocytometer for yeast.
The study reported the organisms were reproducing normally in both 100% H2 and 100% He environment. However, the sigmoid-shaped growth curve was not on par with 100% air. That was because E. coli and yeast switch from ærobic respiration, which uses oxygen, to anærobic respiration and fermentation respectively. Both the processes are less efficient and do not produce enough energy.
E. coli in 80%-20% N2-CO2 environment had slower growth rate as CO2 dissolves and makes the liquid medium acidic. Such reduction in growth rate was not observed for yeast cultures as yeast can thrive in acidic environments. However, yeast’s growth rate in 100% air was far greater than the other three medium. The reason of this significant difference was lack of oxygen, the research reported. Oxygen is essential for synthesis of biochemicals such as heme and sterols, which are important for yeast. In atmospheres lacking oxygen to produce these chemicals, yeast fungi has stunted growth rate.
With this discovery, Dr Seager said scientists can now observe even more planets to study for habitable life.
“There’s a diversity of habitable worlds out there, and we have confirmed that Earth-based life can survive in hydrogen-rich atmospheres […] We should definitely add those kinds of planets to the menu of options when thinking of life on other worlds, and actually trying to find it”, Professor Seager said.
A rocky planet with expanded hydrogen-rich atmosphere is easy to detect using the current technologies. Hydrogen and helium gas have very low density. Dr Seager said “It’s kind of hard to get your head around, but that light gas just makes the atmosphere more expansive […] And for telescopes, the bigger the atmosphere is compared to the backdrop of a planet’s star, the easier it is to detect.”
The research paper highlighted rocky planets which have radius no more than 1.7 times Earth’s radius (Earth’s radius is roughly 6360 km) can produce hydrogen-rich atmosphere, if water were to react with Iron.
The research paper reported E. coli releases a number of gases when it lives in hydrogen-based atmosphere including ammonia, methanethiol, dimethylsulfide, carbonyl sulfide, carbonyl disulfide and nitrous oxide. These gases can serve as biosignature gases which can help astronomers detect and study planets for potential life on exoplanets.
Confirming life can thrive in atmospheres which does not have oxygen, Seager said “Astronomers should keep an open mind as to which planets are worth searching for life”.
Seager said she was happy after confirming the result as she was anticipating the outcome.
With NASA’s James Webb Telescope scheduled to be deployed next year, researchers could observe smaller exoplanets which orbit small red-dwarf planets.