Biofilm formation

• Biofilms


  • Dental plaque
  • Algae on aquarium walls
  • Biofilm on wet stones in rivers/streams
• Biofilm


  A microbial-derived sessile community characterised by cells that are irreversibly attached to a substratum or to each other, are embedded in a matrix of extracellular polymeric substances that they have produced, and exhibit an altered phenotype with respect to growth rate and gene transcription
• Stages of biofilm formation


  Solid surface immersed in water

  2. Covered by primary conditioning film - changes properties of surface

  3. Microbial attachment/adsorption - reversible adhesion

  4. Irreversible attachment - propagation of primary colonisers, loss of motility, microcolony formation, production of extracellular polymeric substances (EPS)

  5. Growth and Division - formation of 3D structures, attachment of other microorganisms (secondary colonisers)

  6. Mature microcolony/biofilm - complex diffusion channels, physiological heterogeneity

  7. Detachment/Dispersion - disintegration, degradation, liberation or detachment of some cells as planktonic cells
• Conditioning film


  • The foundation on which a biofilm grows, can be composed of many particles, organic or inorganic, coated with polymers from the medium
• Reversible adhesion


  • A fraction of the cells reaching the surface reversibly adsorbs and attaches to the surface through nonspecific physicochemical interactions, involving cell appendages like flagella, pili, and fimbriae
• Irreversible attachment


  • Propagation of primary colonisers over the surface, loss of motility, microcolony formation, production of extracellular polymeric substances (EPS)
• Mature biofilm


  • Consists of a nutrient-rich layer which supports rapid growth of microorganisms, complex diffusion channels for transport of nutrients, oxygen and waste products, physiological heterogeneity, EPS more than 90% of the dry mass
• Biofilm dispersal


  Disintegration, degradation, loss of some cells

  2. Liberation or detachment of some cells as planktonic (free-living) cells

  3. Triggered by changes in environmental conditions - temperature change, starvation, oxygen deficiency, and metabolite accumulation

  4. Involves upregulation of genes for cell motility and EPS degradation, and downregulation of genes for EPS production and attachment
• Biofilm dispersal strategies


  • Swarming/seeding dispersal - individual cells released from microcolonies

  2. Clumping dispersal - aggregates of cells surrounded by EPS shed as clumps

  3. Surface dispersal - biofilm structures move across surfaces
• Bacteriophages can cause lysis of biofilm cells, providing a nutrient source and source of extracellular DNA for the EPS matrix
• Extracellular DNA (eDNA) plays roles as an adhesin in initial attachment and stabilisation of mature biofilms, and in structurization by creating channels and cavities