Livne, N. | bioRxiv Science

bioRxiv2025

Single-array measurements reveal non-uniform, mosaic-like chemosensory arrays in bacteria

Motile bacteria use supramolecular arrays to detect effector gradients in their environment. In Escherichia coli, thousands of chemoreceptor molecules with diverse sensory properties cooperatively modulate the kinase activity of these arrays and, via phosphotransfer to a diffusible response regulator, control the cells swimming behavior. Various methods have been used to study these sensory arrays in live cells, from population-level assays to single-cell measurements, revealing hierarchical coupling interactions that underlie their remarkable sensory properties. However, measuring the responses of individual arrays has remained a challenge. Here, by combining the kinase and response regulator into a functional hybrid protein that resides within the array, we directly measured the kinase responses of individual arrays in live cells. These measurements revealed highly diverse and growth-phase-dependent sensory properties of individual arrays. Even arrays within the same cell were not substantially correlated. We also observed dynamic shifts in receptor occupancy within individual arrays. Overall, these data suggest that each array contains a frozen non-uniformity, reflecting its unique assembly history and resulting in a mosaic arrangement of cooperative signaling regions, each with distinct receptor content. Consistent with this view, measured dose-responses of individual arrays mostly exhibit low cooperativity. Interestingly, signal integration in such non-uniform arrays is expected to inherently vary with the size of the cooperative regions.

biophysics↗

bioRxiv2025

Emergence of active turbulence limits chemotaxis-induced collective condensation of bacteria

Collective bacterial condensation arises from positive feedback between the ability of bacteria to generate chemical gradients in their environment and their chemotactic ability to follow those gradients. This feedback drives the spontaneous formation of local cell accumulations, characterized by sharp cell-density gradients, even in the absence of physical boundaries. By following the dynamics of bacterial condensation in uniform acidic environments, we show that condensation is critically constrained by the spontaneous emergence of correlated bacterial swimming and the associated active turbulence. These collective behaviors generate vortex-like cell motion with a pronounced radial component directed down the cell-density gradient. This, in turn, induces local fluid motion that broadens the condensate and expels non-chemotactic bacteria. When condensates are strongly confined in thin layers, the radial component of fluid motion diminishes and condensation is enhanced. Moreover, in porous environments, correlated bacterial motion is strongly suppressed, allowing spontaneous condensation to progress even further until it reaches the limits imposed by the non-local nature of bacterial chemotaxis. Overall, these findings highlight the fundamental interplay between self-generated bacterial condensation and correlated swimming. Significance statementSelf-induced condensation and active turbulence are two prominent forms of collective bacterial behaviors. However, their interplay has not been experimentally studied. Here, we show that collective bacterial condensation gives rise to correlated swimming, which in turn fundamentally limits further condensation. Furthermore, we demonstrate that in dilute porous environments--common in natural bacterial habitats--correlated swimming is strongly suppressed, enabling the spontaneous formation of extremely dense cell condensates. These condensates may serve as a basis for the development of more structured bacterial communities.

biophysics↗