Noisy adaptation enhances bacterial exploration

A distinctive feature of many sensory pathways is their ability to adapt to constant stimuli, thereby extending their dynamic range. The Escherichia coli chemotaxis system, one of the best-characterized sensory networks, maintains sensitivity across five orders of magnitude in ligand concentration through two antagonistic enzymes: CheR, which methylates chemoreceptors to increase pathway activity, and CheB, which demethylates them to decrease activity.

 

Recent single-cell measurements revealed that this pathway operates near a critical point, generating large temporal fluctuations that span its full dynamic range. To probe how adaptation modulates this noise, we combined genetic perturbations with single-cell FRET and found that increasing CheRB expression—while preserving their ratio and thus critical tuning—strongly reduced temporal noise.

 

Tracking swimming cells showed that these changes in CheRB expression did not affect the mean tumble bias but markedly altered the tail of the run-time distribution. Low CheRB levels promoted extended runs, enabling more efficient exploration, whereas high CheRB levels enhanced navigation.

 

In homogeneous nutrient environments, both “explorer” (high-noise) and “exploiter” (low-noise) phenotypes coexist, whereas during collective migration in attractant gradients, low-noise exploiters dominate. This reveals a non-genetic division of labor based on sensory pathway noise.