Scientific Background

      In recent years, microorganisms have been shown to survive and thrive in environments previously thought uninhabitable. Bacteria have been widely documented in the troposphere and cloud droplets contain adequate organic carbon and nutrients to support growth (e.g., Sattler et al. 2001). Initial attempts at biological sampling of the stratosphere used high altitude balloons and meteorological rockets, and bacteria and fungi at altitudes as high as 20 km were first reported over 80 years ago (Rogers et al. 1936). Although the existing body of work on life in the upper atmosphere is impressive and pioneering, it is also very limited and technically primitive. The SMITH project was the first attempt to systematically determine the quantity of cells in the stratosphere.

Table 1: Cellular Stresses - *If background radiation levels are sufficiently
high and ice entrapped population is ancient

      Sampling in the stratosphere will provide information on organisms' ability to survive extreme environments. Environmental conditions (pressure, temperature, and radiation levels) at an altitude of ~100,000 ft are similar to the conditions on the surface of Mars (Table 1). Finding viable organisms in the stratosphere will provide insight to the possibility of life beyond Earth. The MARSLIFE Team continues to develop and test atmospheric sampling payloads that will provide information for future studies for sampling in the atmosphere of Mars.

      In 2010, a low cost sounding balloon payload (HABITAT) tested sampling at altitudes of 10,000 to 30,000 ft. The purpose of HABITAT was to compare the numbers of organisms collected with the existing data. The payloads used silicon grease coated sampling rods (Rotorods, Figure 1) to collect microorganisms during the flight. These rods and the impaction method are commonly used to collect airborne particles for microscopic analysis (e.g. pollen counts). Since we anticipate that the concentrations of cells will be very low at high altitudes, minimizing contamination was critical (Figure 2).

      Using a combination of ultraviolet irradiation, ethanol, sodium hypochlorite, and ethylene oxide, the background level of microbial contamination associated with balloon payload preparation was consistently under 100 cells/ rod, or 1.57 x 106 DNA-containing cells/m2 (i.e. 50 +/- 30 cells per sample rod). The payload was then stored in a sterile bag for housing until flight. During ascent (1000 ft/min) at the target altitude of 10,000 ft, the HABITAT doors opened, allowing the collection of organisms through a specific column of air. The doors closed at ~30,000 ft to end sampling. The rods were returned to the lab and analysis began within 24 hours. Each experiment or assay was completed in triplicate. The rods were analyzed for direct enumeration, counting viable fractions, metabolic activity, culturing, and scanning electron microscopy. These methods allowed us to calculate a number of cells for a given volume sampled.

      The HABITAT and Pirogue missions have taught us many important lessons. Payload protocols have been developed for decontamination, handling and transportation, launch, recovery and analysis. The MARSLIFE team will continue making payloads for biological sampling of the troposphere and stratosphere.

- Noelle Bryan (LSU Biology Department)

References:
Rogers et al. 1936. Rogers, L. A., and F. C. Meier. 1936. U.S.
     Army Air Corps stratosphere flight of 1935 in the balloon "Explorer II," p. 146. The National Geographic Society, Washington, D.C. Sattler et al 2001. Sattler B., Puxbaum H., Psenner R. 2001 Bacterial growth in supercooled cloud droplets. Geophys. Res. Lett. 28, 239-242.