To Find Life on Mars, Make Microbes Wiggle

Could tiny swimming microbes help us unlock the mysteries of extraterrestrial life?

By Gayoung Lee edited by Lee Billings

A color-enhanced microscopic view of Bacillus subtilis bacteria, rod-shaped extremophile microbes commonly found in soil and in the guts of cows and humans.

The latest advance in the search for extraterrestrial life could come from the “wiggles” of swimming microbes—microscopic single-celled organisms that are abundant in just about every nook and cranny of Earth.

Historically, testing for microbial motility has been an expensive and time-consuming task, ill-suited for incorporation into robotic space missions. That’s prompted a team of German astrobiologists to devise a simpler, more cost-efficient way to check for motility, an approach that they have detailed in a study published on February 6 in the journal Frontiers in Astronomy and Space Sciences.

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In their study, the researchers focused on three types of microbes—Bacillus subtilis, Pseudoalteromonas haloplanktis and Haloferax volcanii—all of which are known extremophiles, or organisms that can survive extreme temperatures, pressures or chemical conditions. Their experiment was simple: Could they prompt the microbes to swim toward a nutrient source in a detectable, repeatable way? To do this, they placed microbe-packed water droplets on one partition of a two-chambered microscopic slide. On the other side lay an aqueous solution that was rich with L-serine, an amino acid that is critical for protein synthesis and cell proliferation. When they tested each type of microbe in separate three-hour experimental runs, the researchers could see all three species become motile and migratory: the microbes swam from their initial chamber to form “blobs” inside the chamber with L-serine. This tendency of organism to drift toward or away from the presence of certain chemicals is called “chemotaxis.”

In the case of the organisms used in this experiment, “the idea of chemotaxis is that microbes can sense [and move to] molecules that might be useful for them, especially for metabolism,” explains the study’s lead author Max Riekeles, a Ph.D. student at the Technical University of Berlin. “With our specific setup, we wanted to make the visual and computational aspects [of studying chemotaxis] simpler.”

Such technical advances could be hugely beneficial for future life-seeking space missions, say Nadeau and Lindensmith, both of whom were formerly Riekeles’s colleagues but were uninvolved with the new study. “One of the real problems with doing something like this on another world—especially one that’s going to be very cold, like Europa—is: What happens if those [alien] organisms swim really, really slowly?” Nadeau explains. “Well, in that case you might need to leave them for a week or more and then come back.”

Using the new method, scientists could merely check for any microbes in the nutrient-filled chamber rather than constantly monitoring the system for conspicuously cavorting microbes. “So that part is easy,” Lindensmith says. “The hard part is figuring out what to put on the other side as bait.” Although Earth’s homegrown life may love L-serine and other similarly fundamental foodstuff, there’s no guarantee such substances would be appealing to alien organisms with a different biochemistry.

“You don’t know what’s going to be out there [in space],” Lindensmith says—so diversifying your tools and techniques to scrutinize life right here on our own planet is an important first step. “We have to be able to do all of that kind of stuff on Earth before we can meaningfully do it on other planets.”

Gayoung Lee is Scientific American’s current news intern. A philosopher turned journalist, originally from South Korea, Lee’s interests lie in finding unexpected connections between life and science, particularly in theoretical physics and mathematics. You can read more about her here: https://gayoung-lee.carrd.co

Source: www.scientificamerican.com