What is the connection between metabolism and life detection in space? Metabolic processes and the small molecules (called metabolites) that carry out these functions have caught the attention of astrobiologists. Astrobiologists are scientists who search for evidence of life beyond Earth. These small molecules – such as amino acids, nucleotides, lipids, and sugars – play a big role in the body, and are involved with reactions that produce energy, maintain cellular growth, and help cells react to the environment.
Scientists believe that if they can understand and apply metabolomics, the study of these small metabolites, they can identify signals of basic and common biological processes in places where life itself may be unrecognizable. In this review article, the authors discuss how metabolomics can be valuable to life detection efforts, the instruments used to measure metabolites, and the benefits as well as challenges associated with this scientific field.
What can amino acids, lipids, and other metabolites tell us about life processes? Well, think about metabolites in the context of cells. In cells, we have DNA, which stores our genetic information and is like a code book of our body and how it should work. RNA transcribes, or copies, genetic code and proteins are constructed to carry out these functions. Metabolites effect and alter these functions – communicating, inhibiting or promoting certain actions in response to what is happening in and around the cell.
Since metabolites are so important to cell function, scientists suggest that all potential life in the Universe will need some sort of mechanism like metabolites to carry out basic cell functions. They explore metabolites as possible biomarkers (or the signals of a biological process) of life – whether earthly or extraterrestrial. Additionally, there is the possibility that extraterrestrial life (if present) may use a different genetic code than the one all life on Earth uses – or it may not have DNA or RNA at all. Looking for chemical signs of life through metabolomics is a more direct way to search life in space that does not rely on genetics.
One challenge faced by astrobiologists is telling the difference between biological and nonbiological (called abiotic) reactions. For example, organic compounds that many associate with biology – such as amino acids or nucleotides – can also be created without the help of any living thing. Thus, there is a need to reliably detect the difference between biological and non-biological indicators.
An additional difficulty is time. Looking back at living things long gone is not an easy task. It is even harder when the organism may be disguised, damaged, or degraded by environmental factors. For example, DNA can only survive one million years in most terrestrial environments and a lot of environments in space may have hosted life millions or even billions of years ago. Finally, scientists are still learning about environments in outer space, and what makes an environment able to sustain life. Despite all this, metabolomics offers a way to begin to address these challenges.
First, metabolomics can help scientists understand the connection between the environment and the organisms that live there. For example, on Earth scientists can collect water from an environment of interest, filter it, and catch the small metabolite molecules on the filter for later identification. What scientists find in the water can provide information about the microbes living in the environment and what they are doing.
One instrument scientists use to identify metabolites is a mass spectrometer (MS), which can detect certain kinds of molecules in a sample. Different MS instruments have different strengths and detection ranges. To gather even more information from samples, MS are paired with other instruments to get a complete spectrum of as many molecule types as possible. MS are no strangers to space, and have flown on various missions, including the Curiosity Rover to Mars. Using metabolomic databases and software, data gathered from MS measurements can be recorded, compared, and hopefully, identified.
Second, by studying the metabolites in an environment, scientists can gain information about the possible biologic processes that these small organic compounds might be involved with. In sum, metabolomics can be helpful for life detection by providing strategies for understanding extraterrestrial spaces and the biomarkers that may be present there.
Metabolomics has the potential to be a powerful life detection strategy. It can help scientists put small compounds and their functions into context with the biological system they are a part of (like a cell) and the greater environment. Understanding that relationship can help astrobiologists figure out how to interpret biomarkers and improve the current ways astrobiologists look for life. Although there is still much to learn about what we know and don’t know about biology, one thing is for sure, astrobiology is a promising and exciting field.