extremophiles -- 12/14/22
Today's selection -- from The Next 500 Years: Engineering Life to Reach New Worlds by Christopher E. Mason. What we can learn from organisms that live in extreme conditions:
"What do we know about the limits of life? How far can it go, and how does this translate into the ability to adapt and thrive?
"To address this, we … look to our favorite friends: extremophiles.
"Some extremophiles have adapted to their environments to such a degree that they actually require these environments to thrive. Others, however, are capable of tolerating these extreme environments but would prefer to live in less intense places (extremotolerant), enabling them to visit their more extreme friends. Ideally, through further genetic and cellular engineering, we can make humans and astronauts more extremotolerant. Though there may be a perfect replica of Earth for us to visit one day, either naturally occurring or through our own innovation, living on other celestial bodies in our solar system will require some extensive engineering. Whereas some areas on Mars may fit within Earth's temperature extremes, other planets such as Venus are far hotter than even the hottest recorded temperature on Earth. If we are to enable these extremotolerant abilities within humans, we must first examine Earth's extremophiles.
"The Extreme Microbiome Project, led by Scott Tighe at the University of Vermont, Kasthuri Venkateswaran at NASA, and the Mason lab at Weill Cornell Medicine, is a group of scientists hard at work detailing Earth's extremophiles. This work not only shows us the conditions under which Earth's life can survive, but also reveals the biochemical mechanisms that enable this life to be possible. Once these biological functions of adaptation have been understood, we can then begin to translate them into other systems, such as human bodies, or even other organisms that we will undoubtedly send to other worlds to ensure their survival.
"Extremophiles live across Earth in many different environments, with many types of stressors, including: high/low temperature (thermophile/psychrophile), high pressure (barophile or piezophile), high salinity (halophile), high/low pH (alkaliphile/acidophile), and high radiation (radiophile). Further, endoliths can persist in the microscopic spaces deep within Earth's rocks, aquifers, and fissures, which are also the most likely spots holding life on Mars and other celestial bodies. However, it is also possible that life on Earth began with thermophiles along the hydrothermal vents in the ocean floor (black smokers), and now can be been found in hot springs, hydrothermal vents, and deepsea vents (see below). Notably, Pyrococcus fumaris is a thermophile that was found replicating at 113°C near the walls of black smokers. Other black smokers in China are shown to have arqueobacteria, which can survive at 400°C using chemosynthesis to produce H2S.
"Psychrophiles have specific adaptations to the cold, making them love Arctic and Antarctic climates. Work from Pabulo Rampelotto has shown that their proteins, in general, have more glycine, maintain greater flexibility, reduce their intramolecular interactions with other proteins, and come in smaller fragments -- all to avoid freezing. One paper in 2014 (by Christner et al.) found some archaeal species in Antarctica that seem to require only NH4 + and CH4 for survival, possibly persisting for millions of years in the total absence of sunlight or wind; these adaptations indicate they could even survive on Titan.
"Radiophiles can resist high levels of radiation (both HZE and nuclear).
The 'superman of bacteria,' Deinococcus radiodurans, can withstand radiation up to 5,000 gray (Gy), with no loss of viability, while Thermococcus gammatolerans can survive even higher levels (30,000 Gy). Both can be found hanging out in the cooling waters of nuclear-power plants, as if lounging on a beach chair in the radioactive, microbiological Bahamas. Just as superman has many powers, so do these bacteria -- they can also survive extreme cold, desiccation, a complete vacuum, and even low levels of pH. They are thus known as 'polyextremophiles,' basically polygamous but for extreme states.
"By 2201, a fairly complete catalog of Earth's adaptations and ability to thrive will exist. This will elucidate the genetic source of extremophile powers and be used as a framework to share these powers with other species. While these ideas are already being tested in 2021, such as our own lab's work embedding tardigrade genes into human cells to enable radiation resistance, this full catalog will enable the usage of more powers in more profound ways. These abilities can further be integrated into human cells on artificial minichromosomes, which would enable long-term persistence, no alterations to the protected human genome, and even allow for easy removal. This type of an advanced genetic incorporation system would enable the usage of highly specific modifications at precise timing for unique situations."