Bacillus subtilis Bacteria Generate an Internal Mechanical Force within a Biofilm

Area of Science:

• Microbiology
• Biophysics
• Materials Science

Background:

• Biofilms are a prevalent mode of bacterial life, offering significant resistance and protection.
• The origin of this enhanced resistance in bacterial communities remains a key research question.
• Mechanical properties are hypothesized to play a crucial role in biofilm resilience.

Purpose of the Study:

• To investigate the role of internal forces in the mechanical properties of bacterial biofilms.
• To understand how these forces contribute to biofilm structure, resistance, and behavior.
• To explore the relationship between bacterial growth and the generation of internal stress.

Main Methods:

• Experiments were conducted on pellicles (floating biofilms) of Bacillus subtilis.
• Internal forces and stress within the biofilms were measured during bacterial multiplication and extracellular substance secretion.
• The response of biofilms to mechanical perturbation (cuts or ablation) was observed.

Main Results:

• Bacteria generate an internal force, measured as a stress of -80±25 Pa, during biofilm formation.
• This force is associated with growth-induced pressure, similar to self-equilibrating forces in plants and engineered structures.
• Biofilms exhibited spreading behavior (15-20% increase in size) after ablation, with force relaxation occurring rapidly (milliseconds).

Conclusions:

• Growth-induced pressure is a key factor in the mechanical strength and integrity of bacterial biofilms.
• These internal forces contribute to biofilm shaping, enhanced mechanical resistance, and facilitate invasion and self-repair.
• Understanding these forces provides insight into the prevalence and success of biofilms as a bacterial lifestyle.