The quest for life beyond Earth is one of the most ambitious scientific endeavors. A promising method is to locate motile microorganisms, capable of self-propelled movement, which serves as a strong biological indicator. If such movement is driven by a specific chemical, it is known as chemotaxis.
A team of German researchers has introduced a new and simplified technique to stimulate chemotactic movement in some of Earth's smallest organisms. Their findings have been published in Frontiers in Astronomy and Space Sciences.
"We examined three different bacterial species of microbes and one archaeon, and found that all were attracted to L-Serine," explained Max Riekeles, a researcher at the Technical University of Berlin. "This chemotactic behavior could serve as a strong indicator of life and inform future space missions searching for microbial organisms on Mars or other celestial bodies."
The microorganisms selected for the study were chosen for their resilience in harsh environments. The highly motile Bacillus subtilis, when in its spore form, can withstand extreme conditions, surviving temperatures up to 100 °C. Another species, Pseudoalteromonas haloplanktis, thrives in cold waters, capable of cultivating temperatures ranging from -2.5 °C to 29 °C. Meanwhile, the Archaeon Haloferax volcanii, which shares similarities with bacteria but has distinct genetic differences, naturally inhabits high-salinity environments like the Dead Sea.
"Bacteria and archaea are among the oldest life forms on Earth, but they exhibit distinct motility mechanisms that evolved independently," noted Riekeles. "By including both groups in our study, we enhance the reliability of life detection methods for space exploration."
The study revealed that L-Serine successfully attracted all three species tested. "The use of H. volcanii in this research expands the range of life forms that could be identified through chemotaxis-based detection, particularly as archaea are known to possess chemotactic systems," explained Riekeles. "Since H. volcanii thrives in highly saline conditions, it could serve as an excellent model for potential Martian life."
The researchers developed a simplified technique that improves viability for space missions. Instead of requiring intricate laboratory instruments, their method relies on a slide with two chambers separated by a thin membrane. Microbes are placed on one side, while L-Serine is introduced to the other. "If the microbes are alive and motile, they swim through the membrane towards the L-Serine," explained Riekeles. "This approach is cost-effective, straightforward, and does not demand extensive computing power for analysis."
However, to implement this method on a space mission, certain refinements are necessary. The researchers highlighted the need for compact, robust equipment capable of withstanding the rigors of space travel, as well as automation to operate without human supervision.
If these challenges are addressed, microbial movement could help identify extraterrestrial organisms, such as those potentially inhabiting Jupiter's moon Europa. "This approach could make life detection more efficient and cost-effective, allowing future missions to maximize scientific returns with limited resources," concluded Riekeles. "It represents a practical tool for upcoming Mars missions and complements other direct motility observation techniques."