Self-generated hydrogel ejects bacterial cells for localized biofilm dispersion.

Area of Science:

• Microbiology
• Biophysics
• Biochemistry

Background:

• Biofilm formation is well-studied, but mechanisms of biofilm dispersion remain less understood.
• Enzymatic degradation of the extracellular matrix is a suspected driver of biofilm dispersion.
• Alternative dispersion mechanisms beyond matrix degradation are largely unexplored.

Purpose of the Study:

• To investigate a novel mechanism of biofilm dispersion in Bacillus subtilis.
• To elucidate the role of mechanical forces and specific biomaterials in cell ejection from biofilms.
• To explore the potential for controlling biofilm dispersion through biomaterial modulation.

Main Methods:

• Single-cell resolution imaging was employed to observe biofilm dynamics.
• Mathematical modeling was used to analyze the forces driving cell ejection.
• Chemical and genetic perturbations were performed to identify key molecular components.

Main Results:

• Bacillus subtilis biofilms can eject cells via mechanical forces generated by a self-produced poly-γ-glutamic acid (γ-PGA) hydrogel.
• The production of γ-PGA is essential for this anisotropic cell ejection mechanism.
• Osmotic pressure within the γ-PGA hydrogel propels cells out of the biofilm.
• Modulation of γ-PGA levels allows for control over biofilm dispersion, enabling inhibition or promotion.
• This γ-PGA-driven ejection mechanism is mechanistically similar to processes observed in marine organisms like jellyfish.

Conclusions:

• A novel, mechanically driven biofilm dispersion mechanism involving poly-γ-glutamic acid (γ-PGA) has been identified in Bacillus subtilis.
• This mechanism provides an alternative to enzymatic matrix degradation for biofilm dispersal.
• The findings reveal an unexpected evolutionary parallel between bacterial biofilms and marine invertebrates (Cnidaria).
• The ability to control γ-PGA production offers potential strategies for managing bacterial biofilms.