Interactions Between Snow-Adapted Organisms, Minerals and Snow in a Mars-Analog Environment, and Implications for the Possible Formation of Mineral Biosignatures

Abstract:

Increasing evidence suggests that icy environments on bodies such as Mars, Europa, and Enceladus may be important potential habitats in our solar system. Life in icy environments faces many challenges, including water limitation, temperature extremes, and nutrient limitation. Understanding how life has adapted to withstand these challenges on Earth may help understand potential life on other icy worlds, and understanding the interactions of such life with minerals may help shed light on the detection of possible mineral biosignatures.

Snow environments, being particularly nutrient limited, may require specific adaptations by the microbiota living there. Previous observations have suggested that associated minerals and microorganisms play an important role in snow algae micronutrient acquisition. Here, in order to interpret micronutrient uptake by snow algae, and potential formation of mineral biosignatures, we present observations of interactions between snow algae and associated microorganisms and minerals in both natural, Mars-analog environments, and laboratory experiments.

Samples of snow, dust, snow algae, and microorganisms were collected from Mount Anderson Ridge, CA. Some samples were DAPI-stained and analyzed by epifluorescent microscopy, and others were freeze-dried and examined by scanning electron microscopy, synchrotron X-ray diffraction (XRD) and synchrotron X-ray fluorescence (XRF). Xenic cultures of the snow alga Chloromonas brevispina were also grown under Fe-limiting conditions with and without the Fe-containing mineral nontronite to determine impacts of the mineral on algal growth.

Observations from epifluorescent microscopy show bacteria closely associated with the snow algae, consistent with a potential role in micronutrient acquisition. Particles are also present on the algal cell walls, and synchrotron-XRD and XRF observations indicate that they are Fe-rich, and may therefore be a micronutrient source. Laboratory experiments indicated enhanced algal growth in the presence of nontronite, as well as a close physical association between the snow alga and mineral surfaces. We are presently examining the role of minerals and microorganisms in nutrient acquisition, and attempting to identify mineral biosignatures.