Halophilic Responses to a Range of Salts and their Relevance to Mars

Morwool, Peter Frederick Woolman (2019). Halophilic Responses to a Range of Salts and their Relevance to Mars. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ef11

Abstract

This Thesis investigated the survival of salt-tolerant microorganisms in environments where salts other than NaCl are present, with the aim being to shed new light on the martian astrobiological potential of halophiles.

Salt tolerant microorganisms, “halophiles”, are often proposed as analogues for potential martian life because, for water to exist on, or near, the present-day martian surface requires it to be highly saline. Furthermore, martian salt deposits are often proposed as locations in which to find evidence of ancient martian life; halophiles can undergo “entombment” within salt crystals for indeterminately long periods of time, and there is evidence that this provides protection from the extremes of the martian environment. Both of these proposals, however, are based upon studies of halophiles in terrestrial environments where NaCl is the dominant salt, whereas the martian environment is dominated by a wide range of salt compositions

In this Thesis, Boulby Mine in Yorkshire was studied as its deposits feature a gradual transition from halite (NaCl) to potash (NaCl and KCl in equal concentrations) that might influence the microbial community present. Despite using both culture-independent and culture-dependent techniques, no difference was found in the microbial community across this transition in salt chemistry. It was shown that the NaCl requirement of obligate halophiles, isolated from these deposits, could be lowered by the presence of many other salts (KCl, K₂SO₄, MgCl₂, MgSO₄, Na₂SO₄, CaSO₄). Furthermore, with the exception of MgCl₂, the presence of these dissolved salts facilitated the entombment of viable cells and improved the UV tolerance of entombed microorganisms. This Thesis, therefore, suggests that the presence of non-NaCl salts in a martian environment could support the growth, entombment and survival of organisms analogous to halophiles.