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

Bacteria moving in response to chemical attractants are subject to noise from the environment in addition to that within the cells. Environmental noise is observed typically through fluctuations in the concentrations of the chemoattractant. Interactions between two or more sources of noise may upset the chemotactic motility of the cells. This possibility is investigated here for Escherichia coli through a pair of conditions derived earlier. These conditions relate the tumbling time, the sensing time and the adaptation time of the cells. 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. Keywords: Escherichia coli; chemotaxis; external noise; time constants; feasibility; stochastic resonance Received: 18 August 2009 / Received in revised form: 18 August 2009, Accepted: 31 August 2009, Published online: 22 September 2009