Chapter 13 - Halophilic archaea as beacon for exobiology: Recent advances and future challenges

Abstract

Mars, Enceladus, and Europa are said to have hypersaline environments, which makes a strong case for the studying the exobiological or astrobiological aspects of halophiles. Halophilic archaea–a component of extremophiles, is a natural inhabitant of the hypersaline ecosystems and scores as a unanimous choice for being studied as a model organism in exobiological studies. Apart from ability to survive in salt-saturated conditions, their ability to resist radiation, tolerate dry conditions, adapt to extremes of temperature and pH, and their diverse modes of energy generation that will aid them in adapting to the extreme conditions prevalent in extraterrestrial bodies makes it more compelling to study them. The initial part of this chapter focuses on the missions that have significant contributions to make to exobiological studies. Mariner 4 and Viking 1 & 2 and Phoenix specifically focused on the habitability of Mars in hosting life, whereas while Cassini-Huygens focused on Saturn and its moons, Titan and Enceladus. The next part of the chapter focuses on the specific properties of halophilic archaea that make them an ideal candidate capable of surviving in exoplanets. Halophilic archaea do not solely depend on heterotrophic metabolism, switching over to chemoautotrophy and anoxygenic photosynthesis if necessary. Further, their ability to resist ultraviolet and gamma radiation, to remain viable for millions of years, and to resist perchlorate salt, an abundant element in Mars, could make halophilic archaea survive in exoplanets. The final part of the chapter focuses on the advanced techniques like Raman spectroscopy and microarray chips to study halophilic archaea.