Pseudomonas aeruginosa mechanosensing controls cell polarity during twitching by activating two antagonistic response regulators

Abstract

The opportunistic pathogen Pseudomonas aeruginosa adapts to solid surfaces to enhance virulence and infect its host. Type IV pili (T4P), long and thin filaments that power surface-specific twitching motility, allow single cells to mechanosense surfaces. For example, cells sense T4P attachment to control the direction of twitching motility. In this process, they establish a local positive feedback that polarizes T4P distribution to the sensing pole. A complex chemotaxis-like system called Chp mediates this response. The signalling mechanism allowing for transduction of this spatially-resolved signal is however unresolved. Here we demonstrate that the two Chp response regulators PilG and PilH enable dynamic cell polarization by coupling their antagonistic functions on T4P extension. By precisely quantifying the localization of fluorescent protein fusions, we show that PilG polarizes in response to mechanosensing through phosphorylation by the histidine kinase ChpA. We find that PilH is not inherently required for reversals. However, PilH activation is necessary to break the local positive feedback established by PilG so that forward-twitching cells can reverse. To spatially resolve mechanical signals, Chp thus locally transduces signals with a main output response regulator, PilG. To respond to signal changes, Chp uses its second regulator PilH to break the local feedback. By identifying the molecular functions of two response regulators that dynamically control cell polarization, our work provides a rationale for the diversity of architectures often found in non-canonical chemotaxis systems.