2015 Annual Science Report

SETI Institute Reporting  |  JAN 2015 – DEC 2015

Mars Analogs: Habitability and Biosignatures in the Atacama Deser

Project Summary

This project focuses on the study of habitability in the Atacama Desert of northern Chile, one of the driest regions on Earth. We want to understand how life adapts and survives in an environment where liquid water is exceedingly rare, and how biosignatures are preserved in that environment after microorganisms die. These studies can become a very useful guide for future robotic missions to Mars. This year we focused on microbial communities that inhabit the interior of salt nodules in evaporitic lake deposits. These are the only known active microbial comunities in the driest parts of the Atacama. We wanted to understand how these microbial communities survive in an environment that excludes every other form of life. We suspected that the salt communities use atmospheric water vapor as a source of water to run their metabolic processes. We showed that this is indeed the case with a combination of field and laboratory tools. Our results suggest that the salt substrate could be one of the last possible habitats for life in extremely dry environments.

4 Institutions
3 Teams
3 Publications
1 Field Site
Field Sites

Project Progress

The Atacama Desert of northern Chile is one of the driest regions on Earth, with areas that exclude all plants and animals and where soils have extremely low microbial biomass. However, in the driest parts of the desert there are microorganisms that colonize the interior of salt nodules in evaporitic lake deposits (Figure 1), where they are sustained by condensation of atmospheric water triggered by the salt substrate (aka deliquescence). Using a combination of in situ observations of variable chlorophyll fluorescence and controlled laboratory experiments, we investigated whether this endolithic community is capable of metabolic activity in the extreme dryness of the Atacama.

Figure 1. (A) Elevation map showing the location of Salar Grande (red dotted rectangle) in the Atacama Desert of northern Chile. (B) Panoramic view of Salar Grande (looking south) with salt polygons and nodules in the foreground. (C) Close-up view of a colonized salt nodule. The surface of the nodule shows the typical dark-green colorization due to exposed endolithic communities.

We focused our study on the photosynthetic activity of cyanobacteria found inside the salt nodules. Using a Pulse Amplitude Modulation (PAM) Chlorophyll Fluorometer we monitored in the field when and for how long the cyanobacteria were metabolically active, and how that activity changed with the natural daily cycles. We found that the cyanobacteria inside the nodules were active for periods of at least several days during and after wetting events (Figure 2). We complemented these measurements with laboratory analyses of carbon fixation in the presence of light, and oxygen respiration analyses under dark/light conditions. Together, our results demonstrate that photosynthetic cyanobacteria inside the nodules are a source of organic carbon to the whole community.

Figure 2. Photosynthetic activity measured as quantum yield of PS(II) in freshly exposed interiors of halite nodules for a period of 4 days and 3 nights (black squares). The solid line (T) and dotted line (RH) show the conditions inside a reference nodule measured at time intervals of 10 minutes for the duration of the experiment. Night periods are indicated as dark-grey. An overcast period with fog at the beginning of the experiment is indicated in light grey.
Figure 2. Photosynthetic activity measured as quantum yield of PS(II) in freshly exposed interiors of halite nodules for a period of 4 days and 3 nights (black squares). The solid line (T) and dotted line (RH) show the conditions inside a reference nodule measured at time intervals of 10 minutes for the duration of the experiment. Night periods are indicated as dark-grey. An overcast period with fog at the beginning of the experiment is indicated in light grey.

Overall, our results confirmed that metabolism occurs inside the salt substrate despite the extreme dryness of the Atacama. These results add to a growing body of evidence that as conditions become increasingly dry, living processes are restricted to specialized micro-niches. Ultimately, the capability to actively provide liquid water to the community, and to retain water after a moist event, likely make the salt nodules the ultimate substrates for survival under prolonged and extreme environmental dryness. We think that a similar survival strategy could have evolved on Mars as conditions became increasingly dry, if life ever evolved on the planet. Here, in addition to sourcing liquid water and providing shelter against UV, the salt substrate might also act as antifreeze, thereby expanding the range of conditions compatible with metabolic processes both in terms of water deficit and temperature. Future work will focus on that possibility.

  • PROJECT INVESTIGATORS:
    Alfonso Davila Alfonso Davila
    Project Investigator
  • PROJECT MEMBERS:
    Octavio Artieda
    Collaborator

    Carmen Ascaso
    Collaborator

    Ian Hawe
    Collaborator

    Jacek Wierezchos
    Collaborator

  • RELATED OBJECTIVES:
    Objective 2.1
    Mars exploration.

    Objective 5.1
    Environment-dependent, molecular evolution in microorganisms

    Objective 5.3
    Biochemical adaptation to extreme environments

    Objective 6.1
    Effects of environmental changes on microbial ecosystems

    Objective 6.2
    Adaptation and evolution of life beyond Earth

    Objective 7.1
    Biosignatures to be sought in Solar System materials

    Objective 7.2
    Biosignatures to be sought in nearby planetary systems