Abstract
Microorganisms growing at atmospheric pressures of 0.7 kPa may have a significant impact on the search for life on Mars. Data on their nutrient requirements in a simulated Martian environment are required to ascertain both the potential risk of forward contamination and the potential of past or present habitability of Mars. Serratia liquefaciens can grow at concomitant conditions of low pressure, low temperature, and anoxic atmosphere. Changes in the metabolic fingerprint of S. liquefaciens grown under varying physical conditions including diverse atmospheric pressures (0.7 kPa to 101.3 kPa), temperatures (30 °C or 0 °C), and atmospheric gas compositions (Earth or CO2) were investigated using Biolog GN2 assays. Distinct patterns for each condition were observed. Above 10 kPa S. liquefaciens performed similar to Earth-normal pressure conditions (101.3 kPa) whereas below 10 kPa shifts in metabolic patterns were observed. The differences indicated a physiological alteration in which S. liquefaciens lost its ability to metabolize the majority of the provided carbon sources at 0.7 kPa with a significant decrease in the oxidation of amino acids. By measuring the physiological responses to different carbon sources we were able to identify nutritional constraints that support cellular replication under simulated shallow Mars subsurface conditions.
Highlights
One constraint for robotic or crewed missions to Mars will be the question of whether Earth microorganisms have inherent abilities to survive, grow, and adapt to surface conditions on current-day Mars
The Biolog system was developed for bacterial identification based on species-specific metabolic fingerprints using the differential metabolism of 95 carbon sources[17]
Metabolic activity and substrate richness of Serratia liquefaciens cells were evaluated under different pressures, temperatures, and gas compositions in which one set of conditions simulated a Martian surface environment
Summary
One constraint for robotic or crewed missions to Mars will be the question of whether Earth microorganisms have inherent abilities to survive, grow, and adapt to surface conditions on current-day Mars. Growth of 29 bacterial species under low-PTA conditions[5,6,7] reveals active metabolism and growth at pressures encountered on the Martian surface, and demonstrates the potential that some spacecraft microorganisms may be capable of colonizing hydrated terrains on Mars. Very little data exists on how microbial metabolism is affected by exposure to low-PTA conditions found on Mars. It is unknown whether the same metabolic pathways (e.g., utilization of amino acids versus sugars) are active under low-PTA compared to Earth sea-level conditions. The use of the tetrazolium reduction method allows for the quantification of differential substrate consumption providing estimates on the rates of metabolism on numerous organics under diverse conditions
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