Astrobiologists in Germany are developing a new testing device that could help tease dormant alien microbes into revealing themselves — and its key ingredient is a common amino acid that’s found in abundance inside human blood.
"L-serine, this particular amino acid that we used, [...] we can build it in our bodies, ourselves," researcher Max Riekeles, who is helping to develop the alien-hunting device, told Mashable.
The compound is also prevalent across Earth’s oceans and even down near the dark and otherworldly ecosystems that surround deep sea hydrothermal vents, where life evolved far away from anywhere it could feed itself via photosynthesis. NASA investigators too have found L-serine and similar “proteinogenic” amino acids — which are vital to many organisms’ ability to synthesize their own proteins — buried within meteorites. These and other discoveries have left scientists wondering if any off-world amino acids might have once helped life evolve elsewhere out in the cosmos.
"It could be a simple way to look for life on future Mars missions," according to Riekeles, who trained as an aerospace engineer at the Technical University of Berlin, where he now works on extraterrestrial biosignature research.
“But, it’s always, of course, the basic question: 'Was there ever life there?'"
Riekeles and his team’s device benefits from a phenomena called "chemotaxis," the mechanism whereby microbes, including many species of bacteria as well as another whole domain of microscopic organisms called archaea, migrate in response to nearby chemicals.
Years of research has shown that many tiny organisms have a strong preference for "moving up the L-serine gradient" towards higher L-serine concentrations. This fact led Riekeles and his colleagues to develop their test kit with two chambers divided by a thin, semi-porous membrane: The first chamber would take in a sample from another world, while the second video-monitored chamber would hold a tantalizing concentration of L-serine in water.
“But, it’s always, of course, the basic question: 'Was there ever life there?'"
Granted, the idea of studying single-celled organisms just by watching them move around goes all the way back to the earliest days of microbiology, when Antonie van Leeuwenhoek submitted the first paper on these little beings to London’s Royal Society in 1676.
"Advances in hardware and software the last few years really bring up the really old fashioned way of doing experiments with visual observations," Riekeles said, "especially when you combine it with big data, machine learning and so on."
For their latest experiments, recently published in the journal Frontiers in Astronomy and Space Sciences, Riekeles and his co-researchers focused on three "extremophile" species capable of surviving and thriving in some of Earth’s harshest conditions. Each candidate was selected to approximate the kinds of tiny alien lifeforms that might really live on an inhospitable outer space world — like Mars’ cosmic ray-blasted, desert surface or Jupiter’s icy, watery moons: Europa, Ganymede and Callisto.
"The bacteria Pseudoalteromonas haloplanktis, P. halo, it survives in really cold temperatures, for example," Riekeles told Mashable, "and it’s also tolerant of salty environments."
"And the salty environment, when it comes to Mars, is interesting because there are presumed to be a lot of salts on the Martian surface," he added.
In addition to the microbe P. halo, which was harvested from the oceans off Antarctica and can grow happily at below-freezing temperatures as low as 27.5 degrees Fahrenheit (-2.5 degrees Celsius), the team also tested the bacterial spore Bacillus subtilis and archaeon Haloferax volcanii. A form of gut bacteria found across animal species, B. subtilis develops a protective shell capable of enduring temperatures up to 212 F (100 C). And H. volcanii, found in the Dead Sea and other heavily salted areas, can withstand aggressive radiation exposures, drawing frequent comparisons between it and hypothetical Martian microbes.
"It’s not only salt tolerant," Riekeles noted. "If you don’t put it into an environment where there is salt, it won’t survive."
All three microbes in the study moved from the sample chamber into the test chamber with the L-serine at a fast clip. Within an hour, each produced a "cell density" of roughly 200 percent more microbes in the test chambers that contained about 1.5 grams of L-sirene per liter of water. What's more, B. subtilis climbed to 400 percent more bacteria during tests that doubled the concentration of L-serine molecules.
"We tried, also, other substances, like glucose and ribose," Riekeles added, "but L-serine was, for these three organisms, the most potent."
However, Dirk Schulze-Makuch — a professor of planetary habitability at the Technical University in Berlin, who worked with Riekeles on this project — cautioned that challenges still remain before a device like this can touch down on the Martian surface.
"One big problem," Schulze-Makuch wrote for the website Big Think, "is finding a spot that’s accessible to a lander but where liquid water might also exist."
"The Southern Highlands of Mars would meet these conditions," he said. Another possibility would be low-altitude spots on Mars like the floor of the expansive canyon Valles Marineris or inside caves, where "atmospheric pressures are sufficient to support liquid (salty) water."
