Bistability: requirements on cell-volume, protein diffusion, and thermodynamics

Bistability is a cellular phenomenon observed in bacteria and eukaryotes, linked to functions like enzyme induction and epigenetic switching. Prior research has shown that deterministic and stochastic models often describe bistability, but limitations remain in understanding its physical requirements. No prior work had resolved how cell volume and diffusion influence bistability. This gap motivated an investigation into the physical constraints of bistable systems. Existing models assume well-mixed environments but ignore spatial and thermodynamic factors. It was already known that bistability depends on network architecture and thermodynamic gradients. However, the role of cell size and mixing efficiency remained unclear. This study addresses these uncertainties by mapping known systems onto a biochemical model. The findings aim to clarify how physical parameters shape bistable behavior.

The study aimed to determine the physical requirements for bistability in biological systems. The authors focused on identifying how cell volume, diffusion, and thermodynamics influence bistable switching. They used the Schlögl model as a framework for analysis. The motivation stemmed from gaps in understanding why bistability is limited to certain cell types. The research sought to clarify whether spatial and thermodynamic factors are essential. By simulating spatiotemporal dynamics, the authors tested if mixing and volume affect bistability. They also aimed to distinguish between bistable switching and phase transitions. The study's goal was to map these requirements onto biological systems.

The researchers used the Schlögl model, a well-characterized biochemical framework for bistability. They applied analytical calculations to derive conditions for bistable behavior. Stochastic spatiotemporal simulations were conducted to test these conditions. The simulations varied cell volume and protein diffusion rates. Network architecture was analyzed alongside thermodynamic driving forces. The model included parameters for compartment size and mixing efficiency. The authors compared results from small and large volumes. They assessed how diffusion and volume affect switching behavior.

The strongest finding was that bistability requires small cell volumes and fast protein diffusion. The study showed that large volumes lead to phase transitions instead of bistable switching. Thermodynamic driving away from equilibrium was confirmed as a necessary condition. Fine-tuning of parameters is essential for maintaining bistability. The simulations revealed that mixing efficiency influences switching behavior. Small compartments, like bacterial cells or eukaryotic nuclei, support bistability. Volume changes during the cell cycle may trigger switching events. These results suggest that bistability is fragile and context-dependent.

The authors concluded that bistability depends on small cell volumes and efficient mixing. They proposed that this limits bistable behavior to specific cell types. Thermodynamic driving remains a key requirement for bistability. The findings suggest that volume changes during the cell cycle may trigger switching. Large volumes tend to eliminate bistability in favor of phase transitions. This conclusion aligns with the study's simulations and analytical results. The researchers emphasized the fragility of bistable systems. These conclusions are based on the observed effects of volume and diffusion.