Growth of Bacillus pumilus and Halomonas halodurans in sulfates: prospects for life on Europa

Resumen

The growth of Bacillus
pumilus and Halomonas halodurans under different concentrations of
NaCl, MgCl2 , Na2 SO4 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 pumilus
was cultivated at 0.23 M and 0.33 M NaCl (aw of 0.995 and 0.990,
respectively) while Halomonas halodurans was cultivated at 0.44 M
and 0.89 M NaCl (aw of 0.985 and 0.965, respectively). B. pumilus
seems to accumulate principally betaine while H. halodurans
accumulates 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.