Lecture Notes: Bacteria and Biofilms

Introduction to Bacteria as Communities

• Bacteria were traditionally viewed as individual cells.
• Recent understanding shows bacteria often live in biofilms, not as individuals.
• Biofilms have existed for 3.5 billion years (evidence from fossilized stromatolites).

Biofilms and Human Disease

• Biofilms are significant in chronic infections.
• Bacteria within biofilms communicate via quorum sensing.

Quorum Sensing

• Definition: A chemical communication method allowing bacteria to coordinate group behaviors.
• Coined by: Bonnie Bassler.
• Example: In bobtail squid, quorum sensing triggers light production.
• Pathogens: Can switch from benign to virulent due to quorum sensing.

Mechanism of Quorum Sensing

• Bacteria produce signaling molecules (autoinducers).
• High density of bacteria = high autoinducer concentration = group behaviors activated.

Quorum Sensing Functions

• Virulence Factors: Enzymes for tissue digestion, invasion.
• Competence: DNA uptake.
• Conjugation: DNA transfer between cells.
• Antibiotic Production: Chemical warfare against other bacteria.
• Motility and Group Movement.
• Spore Formation.
• Biofilm Formation.

Biofilm Characteristics

• Group of microorganisms in a slime layer or capsule.
• Common Surfaces: Shower curtains (Ceratia marcescens), dental plaque, catheters, hot springs.
• Biofilm Formation Process:
  • Planktonic bacteria attach to surfaces.
  • Loss of motility, bacteria stay localized.
  • Form towers allowing nutrient/waste flow.
  • Biofilms can detach, spread, and form new colonies.

Biofilms in Nature and Medicine

• Images: Show bacteria and EPS layers in biofilms.
• Clinical Problem: Biofilms require 200x antibiotics to eradicate.
• Nosocomial Infections: 70% associated with biofilms.
• Chronic Infections: Linked to biofilms.

Biofilms in Everyday Life

• Contact Lenses: Require cleaning to remove biofilms.
• Dental Caries: Cavities caused by biofilms.

Positive Uses of Biofilms

• Sewage Treatment.
• Oil Spill Remediation: Using oil-degrading bacteria.

New Discoveries: Viruses and Quorum Sensing

• Viruses (phages) can detect bacterial quorum sensing signals.
• Use this info to determine when to enter lytic cycle.
• Exciting discovery showing viruses can "eavesdrop" on bacterial communication.

Conclusion

• Next lecture will focus on enzymes, metabolism, and biochemical energy processes.