Response coefficient analysis of E. coli chemotaxis to parametric perturbations under the influence of noise

Escherichia coli and other bacteria navigating through ‘open’ environments are under the impact of noise from the environment and from within the cells. This generates fluctuations in the kinetic parameters that characterize the intra-cellular reactions of the chemosensory network, thus affecting the chemotaxis of the cells. This aspect has been studied here for E. coli synthesizing recombinant glucoamylase in a continuous-flow microreactor. Response coefficient analysis (RCA) was applied to a new four-parameter model of the chemotaxis of E. coli. The model considered two types of responses of the cells – linear and adaptive – and two rates of movement of the chemoattractant – slow and fast. Some cells at each position in the microreactor were considered to be moving to the left, some to the right and others in a tumbling state. Striking similarities and differences were observed between the different types of cells, between linear and adaptive responses, and between the kinetic responses to a slow-moving and a fast-moving chemoattractant distribution. One salient observation was that the response coefficients of the left-moving and right-moving sub-populations were mirror images of each other. Tumbling cells either had intermediate characteristics in some situations, as might be expected, or, in other circumstances, resembled the left-moving cells more than they corresponded to the right-moving bacteria. Under certain conditions, cells with normal linear responses exhibited pseudo-adaptive kinetic behavior. Such unexpected observations have been explained. The results offer new insights into possible quantitative effects of environmental noise on the chemotaxis of E. coli and other bacteria.