JW - Microbial Biofilm development Flashcards
What is a biofilm? (4)
- A microbial, sessile community where cells are irreversibly attached to a surface or to each other
- Embedded in a self-produced matrix of extracellular
polymeric substances (EPS) - Exhibit an altered phenotype compared to planktonic cells (e.g., growth rate, gene transcription)
- Often protected from antimicrobials
What are key characteristics of biofilms? (6)
- Organisms embedded in a hydrogel formed by EPS
- Long retention time of cells in close proximity (microconsortia)
- High biodiversity and strong gradients
- Retention of exoenzymes and nucleic acids (large gene pool)
- Increased resistance to biocides, desiccation, and other stresses
- Ability to degrade particulate matter and absorb dissolved nutrients
What is the role of exoenzymes in biofilms? (2)
- Enzymes secreted by cells that function outside the cell
- Aid in nutrient breakdown and biofilm stability
How do nucleic acids contribute to biofilms? (2)
- Bacteria release DNA into the biofilm matrix
- Acts as a structural backbone and increases the gene pool
What is the Impact of bacterial biofilms? (4)
- Important in Bioremediation and biotransformation processes (e.g. wastewater treatment)
- But water reticulation, Biofouling,…
- > 70% of infections are biofilm related
- Have increased resistance
What are some key environmental microbial activities? (4)
- Carbon production and mineralization
- Biofilm formation on living surfaces
- Catalysts for adaptation (e.g., gene transfer, selection pressures)
- Biodegradation
What are some industrial microbial activities? (5)
- Marine fouling - buildup of unwanted microorganisms on submerged surfaces
- Corrosion of metal surfaces
- Wastewater treatment (e.g., trickling filters, activated sludge)
- Fluidised-bed reactors
- Bioremediation of contaminants - natural process that uses microorganisms to clean up contaminated soil, groundwater, and sludge
What are the three stages of wastewater treatment?
Primary:
- Removal of large debris (e.g., stones, rubbish)
Secondary:
- Bacteria convert dissolved solids into settleable solids via:
- Activated sludge (flocs)
- Trickling filters (biofilms)
Tertiary:
- Removal of nitrates, ammonia, phosphates, viruses, and trace chemicals
What is a trickling filter and how does it work? (4)
- Microorganisms grow on stones/plastic as biofilms
- Sewage is trickled over the surface
- Microbes metabolize dissolved organic carbon (DOC) into CO₂ or biomass
- Aeration is critical for maintaining microbial activity
What are some medical and dental biofilms? (2)
- Dental plaque – Bacterial biofilms on teeth
- Chronic wounds – Biofilm-related infections slow healing
How does cystic fibrosis contribute to biofilm formation? (3)
- Genetic disorder causes mucus buildup in lungs (due to dysfunctional transmembrane protein)
- Creates an environment for bacterial biofilms to thrive
- Leads to chronic infections
How do biofilms affect medical implants? (2)
- Form on prosthetic/artificial implants
- Can cause infections that require implant removal
What are the key stages of biofilm development?
- Reversible adsorption – Initial attachment to surface
- Irreversible attachment – Firmly adheres
- Growth – Cells multiply
- EPS production – Biofilm matrix forms
- Increased diversity – Other microbes may attach
What is biofilm dispersal?
Process where bacteria alter gene expression to break down biofilm and disperse
How can biofilm structure be analyzed?
Confocal Laser Scanning Microscopy (CLSM)
- Used to study biofilm architecture and composition
What is the “mushroom model” of biofilms? (2)
- Bacterial biofilms form into mushroom-shaped structures
- Contain water channels that distribute nutrients and oxygen
What is the role of extracellular polymeric substances (EPS) in biofilms? (3)
- Acts as a “glue” holding cells together
- Made of polysaccharides, proteins, lipids, and nucleic acids
- Influences biofilm microenvironment
How does alginate influence biofilm formation? (6)
- Alginate is a component of the EPS
- From pseudomonas aeruginosa
- Stained using TRITC-ConA in CLSM studies
- Helps cells stick together, forming clusters and later mushroom structures:
- Mucoid Phenotype: Bacteria that produce alginate exhibit a mucoid (slimy) phenotype.
- Non-Mucoid Phenotype: Bacteria that do not produce alginate have a non-mucoid phenotype.
What are some key aspects of biofilm biology that have been the focus of research? (6)
- Biofilm life-cycle
- Differentiation in biofilms
- Multicellular traits
- Some microbes form fruiting bodies from where it releases spores e.g. M.xantus
- Communication (quorum sensing)
- Regulate gene expression based on proximity
- bioluminescence controlled by quorum sensing
- Dispersal of biofilm cells
- Recolonisation
What is autotoxic activity in biofilms? (3)
- Biofilm effluents contain self-killing compounds
- May function like apoptosis to benefit the biofilm community
- Some bacteria regulate this via quorum sensing
What is quorum sensing, and why is it important in biofilms? (3)
- A form of bacterial communication based on cell density
- Regulates gene expression and biofilm behavior
- Controls bioluminescence, virulence, and dispersal
What are the main quorum sensing systems in bacteria? (3)
- AHL (AI-1) system – Used by Gram-negative bacteria
- AI-2 system (luxS, luxR) – Present in both Gram-negative and Gram-positive bacteria
- Peptide-mediated regulation – In Gram-positive bacteria (competency, gene transfer, sporulation)
AHL - Acylated homoserine lactone
AI - Autoinducer
What are some bacteria that use AHL-mediated biofilm formation? (6)
- Rhizobium sp. – Nodulation
- Agrobacterium tumefaciens – Colonization, Ti plasmid transfer, invasion
- Erwinia carotovora – Biofilm formation, exoenzyme production, invasion in plants
- Pseudomonas aeruginosa – Swarming, twitching, biofilm formation, dispersal
- Serratia marcescens – Attachment, swarming, biofilm formation
- Aeromonas hydrophila – Mixed-community biofilms
What are some bacteria that use AI-2 mediated biofilm formation? (8)
- E. coli – Biofilm formation
- Vibrio cholerae – Biofilm formation
- Vibrio vulnificus – Biofilm formation
- Bacillus subtilis – Biofilm formation
- Streptococcus mutans – Biofilm development
- Vibrio harveyi – Toxicity to prawns
- Streptococcus gordonii – Mixed-species biofilm
- Porphyromonas gingivalis – Mixed-species biofilm
What are quorum sensing blockers, and why are they important? (3)
- Molecules that inhibit quorum sensing signals
- Block biofilm formation and bacterial communication
- Potential applications in controlling biofilm-related infections
What is phenotypic variation in biofilm dispersal populations? (3)
- Dispersal cells show variation in colony morphology
- This variation is absent in planktonic cells
- May enhance survival in different environments
What is the significance of recolonization in biofilms? (3)
- Variation within biofilm populations increases survival chances
- Homogeneous populations risk complete extinction
- Small colony variants (SCV) show enhanced biofilm formation
What are some applications of biofilm research? (3)
- Industrial & environmental settings: Autotoxic compounds to control biofilms
- Medical settings: Quorum sensing blockers to prevent infections
- Early dispersal in biofilms: Nitric oxide used to induce early dispersal
