Figure 5.

Osmotic challenges and changes in the physicochemistry of the cell. Hypertonicity leads to cell shrinkage and a lowering of the turgor (Δπ); cells plasmolyze when Δπ is zero. During plasmolysis, the cell membrane shrinks away from the cell wall, leading to the collapse of the cytoplasm. The effect of hypertonicity on other physicochemical parameters is indicated in the top right of the figure. Hypotonicity leads to water uptake and swelling of cells, which increases Δπ and ultimately leads to cell lyses. Bottom right: Cryo-EM map of the ABC transporter OpuA at high salt in the presence of cyclic-di-AMP; taken from Sikkema et al. 2020. OpuA accumulates the compatible solute glycine betaine to (sub)molar levels, which counteracts the effect of hypertonic stress.