Characterizing bacterial growth in eutectic and saturated salt solutions relevant to mars

Abstract

Although Mars is a hyperarid environment that poses many challenges to any potential inhabitants, liquid water is available. Many believe this liquid water is formed by the deliquescence of hygroscopic salts. Upon absorbing moisture from the atmosphere, these salts form saturated liquid brines. These extraordinary solutions are capable of remaining liquid even though the surface of Mars is frigid. The salts responsible for the formation of liquids also lower the freezing point. This results in the formation of a eutectic solution. These solutions cannot exist at colder temperatures or acquire any more salt. Even though Mars is dominated by sulfate salts, many believe these eutectic solutions contain high amounts of chlorate and perchlorate salts as well as iron sulfate. These hazardous salts form eutectic solutions at colder temperatures that would cause a sulfate salt eutectic solution to freeze. Regardless, magnesium sulfate eutectic solutions likely exist at or near the surface of Mars. Growth of halotolerant bacteria in media containing 50% w/v epsomite is well documented. Bacterial isolates obtained from Hot Lake, WA and Basque Lake, BC were capable of growth in saturated (~66% w/v) epsomite media at room temperature. These isolates were also capable of growth in saturated (~56% w/v) epsomite solutions at 4°C. Growth occurred at eutectic temperatures and in eutectic solutions. Growth in a eutectic epsomite solution took 50 days. Growth in a potassium chlorate eutectic solution was another attainable goal, given the eutectic point of potassium chlorate occurs at 3% wt at -3°C. Our isolates have demonstrated the ability to grow in 1 M potassium chlorate (~12%). Growth in a potassium chlorate eutectic solution was achieved, another novel laboratory demonstration. Demonstrating that bacteria from Earth are capable of growth in Mars relevant eutectic solutions should concern astrobiologists. The inability to completely sterilize spacecraft may lead to the contamination of Mars or an icy satellite such as Europa or Enceladus.