Osmotaxis in Escherichia coli through changes in motor speed

摘要

Bacterial motility, and in particular repulsion or attraction towardsspecific chemicals, has been a subject of investigation for over 100 years,resulting in detailed understanding of bacterial chemotaxis and thecorresponding sensory network in many bacterial species. For Escherichia colimost of the current understanding comes from the experiments with low levels ofchemotactically-active ligands. However, chemotactically-inactive chemicalspecies at concentrations found in the human gastrointestinal tract producesignificant changes in E. coli's osmotic pressure, and have been shown to leadto taxis. To understand how these nonspecific physical signals influencemotility, we look at the response of individual bacterial flagellar motorsunder step-wise changes in external osmolarity. We combine these measurementswith a population swimming assay under the same conditions. Unlike forchemotactic response, a long-term increase in swimming/motor speeds isobserved, and in the motor rotational bias, both of which scale with theosmotic shock magnitude. We discuss how the speed changes we observe can leadto steady state bacterial accumulation.