| Summary: | We perform quantitative studies of the growth, death, and gene expression of <i>Escherichia coli</i> in a wide range of magnesium sulfate (MgSO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>4</mn> </msub> </semantics> </math> </inline-formula>) concentrations (0–2.5 M). Elevated concentration of MgSO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>4</mn> </msub> </semantics> </math> </inline-formula> causes the inhibition of cell growth, leading to an increase in the population doubling time. We find that cells exhibit three distinct morphological phenotypes—(i) normal, (ii) filamentous, and (iii) small cells at <inline-formula> <math display="inline"> <semantics> <mrow> <mn>1.25</mn> </mrow> </semantics> </math> </inline-formula> M MgSO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>4</mn> </msub> </semantics> </math> </inline-formula>. Filamentous cells arise due to the lack of cell division, while the small cells arise due to the partial plasmolysis of the cells. We further find that cell death starts for salt concentrations >1.25 M and increases with an increasing concentration of MgSO<inline-formula> <math display="inline"> <semantics> <msub> <mrow></mrow> <mn>4</mn> </msub> </semantics> </math> </inline-formula>. For salt concentrations ≥1.66 M, the growth of cells stops and all the cells become smaller than the control cells, suggesting the plasmolysis of the population. Cells grown at salt concentration up to <inline-formula> <math display="inline"> <semantics> <mrow> <mn>2.07</mn> </mrow> </semantics> </math> </inline-formula> M are reversible in both the growth rate and morphology upon the removal of the salt stress. The time scale of reversibility increases with increasing salt concentration. Finally, we investigate the expression of an osmotically inducible gene (<i>osmC</i>), genes involved in magnesium transport (<i>corA</i>), sulfate transport (<i>cysP</i>), and osmotically driven transport of water (<i>aqpZ</i>). We find that a high concentration of magnesium sulfate leads to the upregulation of <i>cysP</i> and <i>osmC</i>.
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