When we search for signs of life beyond Earth, what are we looking for? Do we look for footsteps left by humanoid aliens? Doubtful. Scientists think that if we find life on the icecaps of Mars, the moons of Saturn and Jupiter, or even exoplanets beyond our solar system, it’s most likely that the first signs of life we find are going to be of the microbial variety. But what might that microbial life look like? Should scientists be searching for familiar bacteria? Or maybe life on Mars, Europa, Enceladus, Trappist-1 b, and LHS 1140 b will look totally unlike anything we’ve ever seen.
This is the question Claire Mammoser and her colleagues are exploring as they probe the building blocks of life under extreme conditions. In research presented at the 2017 Experimental Biology Conference in Chicago on Sunday, Mammoser explains how unnatural amino acids may form the basis of yet-to-be-discovered forms of life.
Amino acids are the building blocks of proteins. Scientists know that 20 amino acids make up the proteins in our bodies, but those aren’t the only amino acids that exist on Earth. Mammoser looked at ten others, so-called “unnatural” amino acids that don’t build proteins.
“What sparked our interest in this research is that all of these amino acids, they do exist on Earth, a lot of them,” Mammoser tells Inverse. “But we don’t use them, and the question is, ‘Why?’”
After all, if they don’t form the basis of life, what the heck are they doing here?
“One possible reason is that [natural amino acids] were the only amino acids that were around at the time [we evolved],” she says. “Another reason might be that the amino acids we used were beneficial in some way.” Part of the idea behind this research is that unnatural amino acids could have been better-suited for developing life on other worlds since stability is a basic prerequisite for life.
In an effort to find out whether these unnatural amino acids could have formed the building blocks of life in organisms that evolved on other planets, Mammoser and her fellow researchers in Laura Rowe’s lab at Valparaiso University examined them under the conditions that they could experience on Mars, Europa, and Enceladus: extreme hot and cold temperatures, UV radiation, and pH variations. The researchers also tested five natural amino acids to compare their resiliency under these extreme conditions. They found that many broke down under the extreme conditions, some more than others.
“Far and away, out of everything we tested so far, the one that had by far the highest impact was UV radiation,” says Mammoser. Putting the amino acids under a high-powered UV lamp to simulate conditions on a moon or planet without the atmospheric protection offered by Earth’s atmosphere, many of the unnatural amino acids lost molecular groups.
But this is just the beginning of their research.
Now that the team has established its methods for testing these amino acids, they are really going to get down to business. Mammoser says they want to test the effects of gamma radiation and even higher heat in the future. Specifically, they want to reproduce the high heat and sulfide conditions of an underwater volcano on Earth, known as a black smoker. This would be crucial to understanding how unnatural amino acids could produce chemosynthetic microbes like the ones suspected to live under the surface of Enceladus.
“We’re especially interested in those specific places because of the potential for underwater oceans,” says Mammoser.
Abstract: In addition to the 20 natural amino acids used in the genetic codes of most biological organisms, there are hundreds more non-proteinogenic, or “unnatural” amino acids which could be used in the genetic codes of organisms evolving under conditions different than those on Earth. However, in order for a protein based extraterrestrial life-form to have evolved in the first place, the amino acids within the organism must be relatively stable in the extraterrestrial environmental conditions In this work, the stability of ten unnatural amino acids and five representative natural amino acids has been tested under a variety of extraterrestrial conditions, such as heat, cold, pH variation, and UV radiation. The environmental conditions selected were intended to potentially mimic the conditions on the three most likely locations of life development within our Solar System: the ice caps of Mars, and the subsurface oceans of the moons Europa and Enceladus. After the amino acids were subjected to these conditions while in solution, their stability was quantified using Ultra-Performance Liquid Chromatography with UV-Vis and MS detectors. The area of the parent amino acid peak (determined through MS) on the UV-Vis chromatogram could then be described as a percentage of the area of all non-solvent peaks, with any non-solvent, nonparent peaks representing degradation of the original amino acid. Ultimately, trends in stability could indicate favorable traits for amino acids to possess in order to survive on other planets and moons. Support or Funding Information: This work has been supported by an Indiana Space Grant consortium grant.