E. coli chemosensing accuracy is not limited by stochastic molecule arrivals

Organisms use specialized sensors to measure their environments, but the principles governing their accuracy are unknown. The bacterium <i>Escherichia coli</i> climbs chemical gradients at speeds bounded by the amount of information it receives from its environment. However, it remains unclear what prevents <i>E. coli</i> cells from acquiring more information. Past work argued that chemosensing by <i>E. coli</i> is limited by the stochastic arrival of molecules at their receptors by diffusion, without providing direct evidence. Here we show instead that <i>E. coli</i> encode two orders of magnitude less information than this physical limit. We develop an information-theoretic approach to quantify how accurately chemical signals can be estimated from observations of molecule arrivals as the physical limit and of chemotaxis signalling activity for <i>E. coli</i> cells, and then we measure the associated information rates in single-cell experiments. Our findings demonstrate that <i>E. coli</i> chemosensing is limited by internal noise in signal processing rather than molecule arrival noise, motivating investigations of the physical and biological constraints that shaped the evolution of this prototypical sensory system.