Drift and Behavior of E. coli Cells.

Area of Science:

• Microbiology
• Biophysics
• Systems Biology

Background:

• Chemotaxis in Escherichia coli is well-understood in shallow chemical gradients.
• Swimming behavior in steep chemical gradients remains difficult to interpret.
• Existing theories often rely on perturbation approaches suitable for shallow gradients.

Purpose of the Study:

• Investigate the dependence of chemotactic drift velocity on attractant concentration in steep gradients.
• Explore the limitations of bacterial chemotaxis beyond shallow gradient approximations.
• Understand the role of finite receptor-methylation sites in adaptation.

Main Methods:

• Single-cell trajectory analysis from simulations.
• Investigation of bacterial behavior in exponential chemical gradients.
• Experimental validation using microfluidics to create controlled chemical gradients.

Main Results:

• Drift velocity maxima in steep gradients exceed predictions from linear-response theory.
• Finite receptor-methylation sites limit adaptation and drift.
• Observed a novel phenomenon of cells 'pinning' to specific concentrations where methylation sites are saturated.

Conclusions:

• Bacterial chemotaxis in steep gradients exhibits behaviors not explained by shallow gradient theories.
• Finite receptor capacity is a critical factor limiting chemotactic performance.
• Experimental validation confirms simulation findings on drift velocity limitations and pinning effects.