Science Highlights – Fall 2020

December 18, 2020

Polar Microbes Give Peptide Clues For Detecting Life on Icy Worlds 

Daniel Larsen & Brook Nunn

Plumes of water ice and vapor erupting from cracks on an icy body and connect the subsurface ocean to the moon’s surface. Bacteria living in the ocean could get trapped in brine pockets as the water freezes and ejected through the plume. Peptide biomarkers from that bacteria could be then detected by future flyby or lander missions to the moon. (Image Credit: Brook Nunn)

Many bodies in our solar system are known to contain water, usually as a vapor in their atmosphere or frozen out on their surface, but some of the moons around the gas giant planets are hypothesized to contain subsurface liquid oceans deep beneath their icy crusts.  Observations from spacecraft, such as the Voyager and Kepler missions, have found the surfaces of these bodies to be dynamic, with fresh ice forming as the subsurface liquid seeps through cracks and geysers in the crust.  Life as we know it on earth requires liquid water to survive, yet can withstand subzero temperatures and high salt conditions, such as those found in microscopic brine pockets that form as ocean water freezes.  If life is present in subsurface oceans on icy worlds or trapped in similar brine pockets in the ice, can we use these Earth-analog systems to understand what to look for in our search for life elsewhere? Are there detectable biomarkers here on Earth that can guide our search life on other frozen planetary surfaces? These are questions that an exciting recent study, led by several UWAB faculty members and alumna, has attempted to answer. 

In this study, current UWAB faculty member, Brook Nunn (Genome Sciences), along with former UWAB faculty member, Jon Toner (ESS), UWAB Alumna Marcela Ewert (Dual-Title PhD Oceanography & Astrobiology, 2013), former UWAB student Erin Firth (MS Oceanography, 2015), Karen Junge (UW Polar Science Center), and their team members studied the marine, cold loving, bacteria, Colwellia psychrerythraea strain 34H (Cp34H), subjecting it to varying levels of nutrients, temperatures, and salinity over different lengths of time. Through this multi-department collaboration, this study provides new insight regarding how psychrophiles (or cold loving organisms) respond to the specific constraints of temperature and/or salinity on life in the extreme, and often very salty, cold on Earth and thus possibly in subzero environments of other bodies in our solar system, for instance on Mars, Europa, and Titan.

The results of this study showed several things, including that high salinity, rather than decreased temperatures, were the most detrimental to cells, while higher levels of nutrients were found to play a critical role in the long-term viability of the bacteria under subzero conditions.  Perhaps, more interestingly, the proteomic analysis of each condition showed a distinct condition-specific protein signature, suggesting that the bacteria are forced to employ a unique suite of metabolic changes in order to survive in the various conditions.  This allowed the investigators to present condition-specific protein biomarkers that could be detected here or off-Earth as indicators of the environmental condition in which they thrive. 

Figure S4. Proteins identified via mass spectrometry to undergo significant changes in abundance compared to optimal conditions were mapped to functional orthology enrichment terms using EggNog. A count was determined (shown in individual boxes) for each experimental condition to identify differences between temperature, salinity, and nutrient
responses

In the polar regions here on Earth, as ocean water freezes the salts dissolved in the water are forced into small pockets of liquid water trapped in the ice structure.  These brine pockets thus have a far larger level of salinity than the ocean water, which keeps the water in a liquid state, despite its temperature dropping below the freezing point.  With subsurface oceans suspected on bodies elsewhere in our solar system these brine pockets are likely to be analogous to environments found in the icy crusts of those bodies.   It is therefore critical to understand how organisms here on Earth survive these conditions and what molecules might be used as indicators of life that has had to adapt to similar conditions elsewhere.

This study supports the possibility that not only might bacteria from the subsurface ocean be able to survive the harsh conditions of a supercooled, low nutrient, brine pocket within the frozen crust, but also, if that bacteria were able to make its way to the surface of the ice (such as through the plumes erupting from the crust of Enceladus), proteomic analysis of the ice could identify the elevated levels of proteins or peptides (fragments of proteins) that the bacteria was producing.  These proteins would then serve as clear biomarkers that could be detected by a probe sent to the planet’s surface or collected in a flyby through an erupting plume.

The team plans to expand on their research and conduct similar analysis of conditions analogous to ice found on, or just below, the surface of Mars!

Publications

Presentations

  • Jacob Lustig-Yaeger (Astro) gave an invited talk on “The Era of Terrestrial Exoplanet Characterization” at the Fall 2019 AGU conference in San Francisco in a Joint AGU-AAS Session on Frontiers in Exoplanets.
  • Andrew Shumway (ESS) gave a public talk through UW Engage Science as the culmination of a science communication program.  He explained how the presence of salts on Mars might mean there could be liquid water available for life. Watch a Recording of the Presentation Here
  • Zac Cooper (Ocean) gave a presentation during the Biological Oceanography Lunch Seminar covering the topics of his thesis proposal. The title of his presentation was “Microbial evolution and ecology in subzero hypersaline environments”.
  • Several UWAB and VPL team members attended and presented at the Exoplanets III conference at the end of July which was scheduled to be in Heidelberg, Germany, but was moved to a virtual format! Profs. Vikki Meadows & Eric Agol (Astro) also served on Scientific Organizing Committee for the conference!
  • Andrew Lincowski and Samantha Gilbert (Astro) presented talks for the Virtual TRAPPIST Habitable Atmospheres Intercomparison (THAI) Workshop
  • Dr. Roy Black (Chem) presented a talk, entitled “Prebiotic membranes bind protocell building blocks and catalyze formation of biopolymers” at the Molecular Origins of life, Munich 2020 virtual conference.
  • Postdoc Mike Wong (Astro) wrote a guest blog post for the NExSS-funded website Many Worlds.  You can read the blog post here.
  • Dominic Sivitilli (Psych) gave a TEDxSeattle talk about his ongoing research of Octopus and using them as a possible model of intelligent life in the universe. You can watch the presentation here.