Abstract
Sodium and sulfate ions are among the suggested abundant ions on Europa, a moon of Jupiter. In order to investigate the potential habitability of Europa, we study the effects of sodium sulfate (Na2SO4) on a non-halophilic bacterium by subjecting Escherichia coli (E. coli) to a wide range of Na2SO4 concentrations (0–1.0 m). We discover that, as the concentration of sodium sulfate increases, the biomass doubling time increases and the cell growth is completely inhibited at m Na2SO4. Furthermore, we find that E. coli exhibits three distinct morphological phenotypes—(i) shortened, (ii) normal, and (iii) elongated/filamented cells at m and m Na2SO4. We have examined the expression of different genes involved in sodium and sulfate transport (nhaA, nhaB, cysZ, sbp), osmotically driven transport of water (aqpZ), sulfate metabolism (cysN), fatty acid production (fabA), and a global transcriptional regulator (osmZ). Our results suggest that the expression of these genes is not affected significantly at high concentrations of sodium sulfate in the exponential growth phase. Using our experimental data and the existing data in the literature, we show that the osmotic pressure difference may play a major role in determining the growth inhibition of E. coli and B. subtilis at high concentrations of salt.
Highlights
Environmental conditions, such as high temperature, high pressure, hypersalinity and extremes of pH, are considered hostile to humans
We have studied the effect of high concentrations of sodium sulfate on cell growth, death, morphology, cell division, and gene expressions of a halotolerant bacterium E. coli
We find that E. coli can tolerate moderately high concentrations of sodium sulfate
Summary
Environmental conditions, such as high temperature, high pressure, hypersalinity and extremes of pH, are considered hostile to humans. A combination of surface observation by Galileo’s near-infrared mapping spectrometer (NIMS) and geochemical modeling suggests a range of ionic composition of Europa’s ocean [19–25]. The subsurface ocean of Europa is hypothesized to be saline with the presumed abundance of Na+ , SO24− , Mg2+ , and Cl−. A geochemical model by Marion et al places the Na+ and SO24− concentrations in Europa’s ocean to be 1.6 M and 3.6 M, respectively [26]. Since Europa’s surface is relatively young and active, it is suggested that the surface chemical composition may be indicative of the composition of the subsurface ocean and the evidence for potential habitability of the ocean
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