Observing mechanosensitive channels in action in living bacteria

Area of Science:

• Biophysics
• Cell Biology
• Microbiology

Background:

• Mechanosensitive (MS) channels are crucial for cellular protection against osmotic stress by regulating the cytoplasmic membrane (CM).
• Understanding the dynamic states of MS channels is vital for comprehending cellular responses to environmental changes.
• Existing methods for observing MS channel activity can be limited in their ability to provide real-time, non-invasive measurements in living cells.

Purpose of the Study:

• To demonstrate the utility of time-resolved second-harmonic light scattering (SHS) for observing the open-closed states of MS channels in living bacteria.
• To investigate the transport dynamics of molecules across the bacterial CM as a function of MS channel activity.
• To validate SHS findings using complementary experimental and computational approaches.

Main Methods:

• Utilized time-resolved second-harmonic light scattering (SHS) to monitor the transport of malachite green cations across the bacterial CM.
• Manipulated MS channel states through osmotic shock (transient and persistent) induced by altering the suspension medium.
• Corroborated SHS results with numerical model simulations and fluorescence-based assays using propidium iodide.

Main Results:

• SHS effectively distinguished between open and closed states of MS channels in living bacteria.
• Malachite green cation transport across the CM was at least two orders of magnitude faster when MS channels were open compared to closed.
• Fluorescence experiments confirmed that cell staining with propidium iodide was dependent on the MS channel state, with open channels facilitating staining.

Conclusions:

• Time-resolved SHS is a powerful, non-invasive technique for real-time monitoring of MS channel activity in living bacteria.
• The study provides quantitative insights into the role of MS channels in regulating membrane permeability during osmotic stress.
• SHS offers a valuable alternative or complementary method to traditional techniques like patch-clamping for studying ion channel dynamics.