Determining the environmental resolution and cellular heterogeneity of quorum-sensing bacteria.
Abstract
Bacteria can be highly social organisms, communicating and cooperating within multi-cellular groups. These social behaviors are often coordinated by a cell-cell communication system termed quorum sensing (QS), which allows bacteria to coordinate collective behaviors including virulence. Small signal molecules are released and act as environmental probes, accumulating, diffusing and decaying as a function of the social and physical environment. Subsequent detection of signal molecules can result in large-scale gene regulatory shifts, turning on the production of secreted enzymes and toxins that can collectively restructure the extracellular environment. QS is intrinsically a multi-individual phenotype, yet most QS research has focused on intracellular genetic architecture, leading to a detailed understanding of the regulatory mechanisms shaping the production of and response to signal molecules within bacterial cells. The current proposal aims to address the persistent gap in QS research between intracellular regulatory mechanisms and multi-cellular phenotypes. Specifically, seeking to determine how multi-cellular behaviors are built from variable single-cell contributions and distinct environmental contexts. While the traditional QS paradigm states that QS-controlled behaviors are governed by a critical threshold cell density or ÔquorumÕ, a growing number of studies point to non-uniform responses in response to controlled signal variation. Using the opportunistic human pathogen Pseudomonas aeruginosa (PA), pilot data illustrates smoothly varying collective responses to environmental variation (varying stationary phase density), built from shifting proportions and intensities of individual cells in an QS active state. In short, this data indicates there is no threshold ÔquorumÕ on either the individual or collective scale. In light of this pilot data, the central hypothesis is that quorum sensing enables bacteria to deliver graded collective responses to variation in both physical and social environments via shifting bimodality in single cell QS activity through time. The proposal will address the hypothesis via the following specific aims: Aim 1. Determine the individual and collective quorum sensing responses to varying density and mass transfer environments. To map the environmental resolution of P. aeruginosa QS, aim 1 will track single-cell and collective QS behaviors across graded variation in population density and dilution rate. The project will focus on density and dilution (mass-transfer) as these dimensions are at the heart of debate over the functional role(s) of QS, and can be precisely and independently controlled via chemostat experiments. Aim 2. Determine single-cell temporal dynamics under defined signal environments and genetic manipulations. The destructive ÔsnapshotÕ sampling approach in Aim 1 does not provide information on the timescale of individual cell commitment to QS states. Aim 2 seeks to resolve the temporal dynamics of individual cell QS responses to defined signal exposures via non-destructive microfluidic imaging platforms (mother machines), on both intra- and inter-generational scales. Impact. The project is directly responsive to the ArmyÕs research goals as stated in the current BAA, including on Ôbiological systems for sensing and detectionÕ, and ÔBottom-up analysis of information exchange, signaling interactions and structure-function relationshipsÕ. The project will determine how PA integrates information on its physical and social environment via multi-signal QS processing, and how this information governs heterogeneous behaviors on the single-cell scale. Together this body of work will provide a platform to address QS function(s) across bacteria on both the single-cell and collective scales, and connects to applied concerns from infection management to synthetic biology control of bacterial communities. Page C-
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 19, 2023
- Source ID
- W911NF2310140
Entities
People
- Samuel M Brown
Organizations
- Army Contracting Command
- Georgia Tech Research Corporation
- United States Army