Halophilic archaea on Earth and in space: growth and survival under extreme conditions

Abstract

Salts are abundant on Mars, and any liquid water that is present or may have been present on the planet is expected to be hypersaline. Halophilic archaea (family Halobacteriaceae) are the microorganisms best adapted to life at extremes of salinity on Earth. This paper reviews the properties of the Halobacteriaceae that may make the group good candidates for life also on Mars. Many species resist high UV and gamma radiation levels; one species has survived exposure to vacuum and radiation during a space flight; and there is at least one psychrotolerant species. Halophilic archaea may survive for millions of years within brine inclusions in salt crystals. Many species have different modes of anaerobic metabolism, and some can use light as an energy source using the light-driven proton pump bacteriorhodopsin. They are also highly tolerant to perchlorate, recently shown to be present in Martian soils, and some species can even use perchlorate as an electron acceptor to support anaerobic growth. The presence of characteristic carotenoid pigments ( α -bacterioruberin and derivatives) makes the Halobacteriaceae easy to identify by Raman spectroscopy. Thus, if present on Mars, such organisms may be detected by Raman instrumentation planned to explore Mars during the upcoming ExoMars mission.

MIR, VNIR, NIR, and Raman spectra of magnesium chlorides with six hydration degrees: Implication for Mars and Europa

“…Magnesium chlorides with different hydration states are potentially distributed widely on the surface and within the subsurface of Mars and Europa. [1][2][3][4][5][6][7][8] On Mars, the subsurface of Cl-bearing salts (including hydrous magnesium chlorides) can be potential source materials for RSL due to the fact that their deliquescence can occur in an RH range that is much lower than those required by hydrous sulfates. [12][13][14] On Europa, with the extremely low surface temperature, the hydrated magnesium chlorides would be mixed with other salts (e.g., Mg-sulfates) and H 2 O ice.…”

“…The data from the wet chemistry laboratory on board of Phoenix lander also suggest high concentration of chlorides (and perchlorate) at the Phoenix landing site. [4] Mars-and Europa-related chloride salts potentially include [5][6][7][8] sodium chloride (NaCl), magnesium chloride (MgCl 2 ), calcium chloride (CaCl 2 ), and potassium chloride (KCl). At the same time, modeling study [9,10] suggests that detection of chloride and perchlorate at the Phoenix landing site is associated with calcium and magnesium.…”

Carotenoids from Haloarchaea and Their Potential in Biotechnology

“…The presence of characteristic carotenoids (α-bacterioruberin and derivatives) in haloarchaea cells is easy to identify by Raman spectroscopy [ 30 , 92 , 93 ]. Thanks to this technique, α-bacterioruberin has been identified as the mayor carotenoid in the following haloarchaea: Halobacterium salinarum strains NRC-1 and R1, Halorubrum sodomense , Haloarcula vallismortis [ 78 ] and Haloarcula japonica (68.1% of the total carotenoids (mol %) [ 5 ] .…”

“…Within the halophiles there is a family of particular interest in several fields of applications: micro-ecology, biotechnology and extreme metabolic adaptations. This is the case of the Haloferacaceae family (previously mentioned) grouping extreme halophilic archaea inhabiting salty environments such as marshes or salty ponds from where NaCl is obtained for human consumption [ 27 , 28 , 29 , 30 ]. The first study about carotenoid production by halophilic microorganisms from the Haloferacaceae family (previously called Halobacteriaceae family ) were published in the latter half of the 1960s [ 31 , 32 ].…”

Characterization of a novel ω-transaminase from a Triassic salt mine metagenome

“…Based on the BLASTp results, where the closest neighbor was a protein from the halotolerant bacterium, Halomonas utahensis, coupled with characterization of enzyme performance under varying reaction parameters, it can be assumed that KMG-TAm4 is derived from the DNA of a bacterial species. Unlike their haloarchaeal counterparts [35][36][37][38]., the enzymes and intracellular machinery of halotolerant bacteria aren't necessarily adapted to high salt concentrations, largely excluding salt from the cytoplasm and replacing it with other 'compatible solutes' [39][40][41]. This perhaps provides a cautionary tale that genomic mining from extreme environments will not necessarily deliver enzymes which exhibit extreme adaptations.…”