Physicochemical homeostasis in bacteria

Abstract

In living cells the biochemical processes such as energy provision, molecule synthesis, gene expression and cell division take place in a confined space where the internal chemical and physical conditions are different from those in dilute solutions. The concentrations of specific molecules and the specific reactions and interactions vary for different types of cells, but a number of factors are universal and kept within limits, which we refer to as physicochemical homeostasis. For instance, the internal pH of many cell types is kept within the range of 7.0 to 7.5, the fraction of macromolecules occupies 15-20% of the cell volume (also know as macromolecular crowding) and the ionic strength is kept within limits to prevent salting-in or salting-out effects. In this article we summarize the generic physicochemical properties of the cytoplasm of bacteria, how they are connected to the energy status of the cell, and how they affect biological processes (Figure 1). We describe how the internal pH and proton motive force are regulated, how the internal ionic strength is kept within limits, what the impact of macromolecular crowding is on the function of enzymes and the interaction between molecules, how cells regulate their volume (and turgor), and how the cytoplasm is structured. Physicochemical homeostasis is best understood in Escherichia coli, but pioneering studies have also been performed in lactic acid bacteria.

Macromolecular Crowding, Phase Separation, and Homeostasis in the Orchestration of Bacterial Cellular Functions

“…We present the physicochemical homeostasis in connection to the volume regulation of the cell, because osmotic perturbations offer a means to alter and study the physical and chemical state of the cytoplasm. Moreover, osmotic up- or downshifts affect the macromolecular crowding and apparent viscosity, internal pH, ionic strength, and turgor pressure, and it is almost impossible to separate these properties from each other (see extended abstract published in Poolman 2023) . Finally, we connect the physicochemical homeostasis to the energy status of the cell and focus on various interdependencies of these cellular parameters rather than on the mechanisms of the (membrane) proteins involved [for comprehensive reviews on these topics, we refer to refs − ).…”

“…Hypotonicity leads to water uptake and swelling of cells, which increases Δπ and ultimately leads to cell lysis. Figure modified from ref . Copyright the Author(s) 2023.…”

The Impact of Physicochemical Conditions on Lactic Acid Bacteria Survival in Food Products

“…Bacterial proteins along with ribosomal RNA are spaceconsuming and therefore reduce cell volume [69]. When cells are under environmental osmotic stress osmoregulatory transporters are activated and ionic concentration changes as well as ionic strength [70,71]. Dehydration and the associated osmotic stress lead to a decrease in the bacterial cell volume, an increase in ionic strength and crowding, and a decrease in cell turgor.…”

Osmotic stress as a factor for regulating <i>E. coli</i> hydrogenase activity and enhancing H₂ production during mixed carbon sources fermentation

“…Cell turgor is the hydrostatic pressure difference that balances the difference in internal and external osmolyte concentration [23] . Due to the small size of bacteria, turgor is experimentally quite difficult to determine, and with the use of different techniques, values for the magnitude of turgor in Escherichia coli differing by a factor of ten have been reported; values range between 30 kPa (0.3 atm) (42) and 300 kPa (3 atm).…”

“…No microorganism can actively pump water into or out of the cytoplasm to compensate for the osmotically instigated water fluxes across the cytoplasmic membrane. Hence, cellular adjustments to both hyper- and hypoosmotic stress must rely on indirect countermeasures that allow the cell to direct and scale water influxes or effluxes as the environmental osmolality fluctuates [23] .…”