Growth ofBacillus pumilusandHalomonas haloduransin sulfates: prospects for life on Europa

The growth ofBacillus pumilusandHalomonas haloduransunder different concentrations of NaCl, MgCl₂, Na₂SO₄ and MgSO₄ was investigated. The objective was to demonstrate whether these cultures have the ability to grow, not only in media enriched with sodium chloride, but also with other salts of astrobiological interest. The importance of this monitoring was to evaluate the fitness of these strains to the hypothetical salt content and composition of extraterrestrial sites, such as the ocean of Europa, one of the satellites of Jupiter. The mechanism of fitness used by these bacteria was investigated by characterizing the compatible solutes accumulated by each strain.Bacillus pumiluswas cultivated at 0.23 M and 0.33 M NaCl (awof 0.995 and 0.990, respectively) whileHalomonas haloduranswas cultivated at 0.44 M and 0.89 M NaCl (awof 0.985 and 0.965, respectively).B. pumilusseems to accumulate principally betaine whileH. haloduransaccumulates betaine and glutamate, depending on the salt content of its environment. These results are discussed in the context of the salinity and salt composition of Europa’s ocean and under their implications for the habitability of this Jovian satellite.