A feasibility analysis of bacterial chemotaxis under the influence of external noise

Bacteria moving in response to chemical attractants are subject tonoise from the environment in addition to that within the cells.Environmental noise is observed typically through fluctuations inthe concentrations of the chemoattractant. Interactions between twoor more sources of noise may upset the chemotactic motility of thecells. This possibility is investigated here for Escherichia colithrough a pair of conditions derived earlier. These conditions relatethe tumbling time, the sensing time and the adaptation time of thecells. It is observed that chemotaxis is not feasible if the normalized variance of the external noise exceeds a critical value. This critical value does not depend on the expression of CheR, a key protein in the chemosensory system, and it agrees with similar values reported by others for intra-cellular noise. These observations indicate that stochastic resonance may be a prime factor enhancing chemotaxis in the presence of noise.