Chemotactic Migration of Escherichia Coli to Glucose is due to Additive Contributions from Phosphotranspherase System and Trg Receptor Sensing Mechanism

Abstract

The chemotactic response of Escherichia coli to glucose is mediated by two distinct intracellular mechanisms, namely, a receptor mediated response through Trg, and a PhosphoTransferase System (PTS) sugar uptake mechanism. The study by Neumann et al. (www.pnas.org/cgi/doi/10.1073/pnas.1205307109) has recently demonstrated that the signals from the PTS and the Trg sensing mechanism is integrated to yield an additive intracellular response in E. coli wherein the relative kinase activity is weaker for the PTS compared to the Trg mediated response. While this additive property, through the two mechanisms, has been shown at the signalling level, its consequence on the chemotactic migration of a population of cells remains to be demonstrated. We performed experiments with a wild type E. coli K12 strain and a mutant lacking Trg to determine the drift velocity at various locations along a micro-capillary for varying gradients of glucose and, a non-metabolizable analogue of glucose, 2-Deoxy-D-glucose. The experiments demonstrated that the individual and integrated contributions of the two mechanisms at the intracellular level in response to glucose is closely reflected at the phenotypic level. We also measured the run speed, clockwise bias, cell diffusivity, and relate these measurements to the two mechanisms. We compare the chemotactic response obtained for glucose with that obtained for L-serine and Methyl-aspartate.