MCB 150 Biofilms, etc.

• Biofilm


  Functional and growing microbial assemblages attached to a surface and enclosed in an adhesive polysaccharide matrix that is the product of excretion by cells and cell death

  
• Planktonic cells


  Motile, floating or free-living cells
• Microbial mats


  Extremely thick biofilms
• Biofilms can be found where moisture and nutrients are present

  
• Biofilm matrix is typically a mixture of polysaccharides, proteins, and nucleic acids that bind the cells together
• Biofilms may contain only one or two species or, more commonly, many species of bacteria
• Functional consequences of bacterial life in biofilms


  • Enhanced protection against shear stress, desiccation, toxic compounds, and protozoan grazing
  • Trap nutrients for microbial growth
  • Help prevent the detachment of cells on dynamic surfaces, such as in flowing systems

  
• Human bacterial infections are often linked to pathogens that develop in biofilms during the disease process
• Biofilms are a major problem in industry since they cause fouling of equipment, damage to water distribution facilities, contamination of fuels, and souring from chemicals

  
• Factors Affecting Biofilm Formation


  • Substratum effects
  • Characteristics of the aqueous medium
  • Cell properties
  • Hydrodynamics/Flow velocity

  
• Surface texture


  Microbial colonization increases as the surface roughness increases
• Surface material


  Microorganisms attach more rapidly to hydrophobic, nonpolar surfaces
• Conditioning film


  A material surface exposed in an aqueous medium will inevitably and almost immediately become conditioned or coated by polymers from that medium, and the resulting chemical modification will affect the rate and extent of microbial attachment
• Ionic strength


  An increase in the concentration of several cations (sodium, calcium, lanthanum, ferric iron) was shown to affect attachment by reducing the repulsive forces between the negatively charged bacterial cells and the surfaces
• Nutrient level


  An increase in nutrient concentration correlated with an increase in the number of attached bacterial cells
• Cell properties


  • Presence of fimbriae and flagella, and production of EPS enable the cell to remain attached until more permanent attachment mechanisms are in place
  • Surface hydrophobicity increases interaction for attachment
• Hydrodynamics/Flow velocity


  As the velocity increases, the cells will be subjected to increasingly greater turbulence and mixing
• Biofilm Formation


  1. Reversible attachment

  2. Transition to irreversible attachment

  3. Maturation-I stage

  4. Maturation-II stage

  5. Dispersion

  
• Microcolony


  The basic structural unit of the biofilm, providing an ideal environment for the formation of nutrient gradients, exchange of genes, and cell-to-cell signaling

  
• Microcolonies may be composed of several species, which allows the cycling of various nutrients (e.g. nitrogen, sulfur, and carbon) through redox reactions
• Biofilms are very heterogeneous, having microcolonies of bacterial cells encased in an Extracellular Polymeric Substances (EPS) matrix and are separated from other microcolonies by interstitial voids
• EPS vary in chemical and physical properties but is primarily composed of polysaccharides, which provides the binding force in a developing biofilm
• Organisms in specific environments


  • Anaerobic bacteria like Gardnerella vaginalis and Atopobium vagnae causing Bacterial vaginosis
  • Salmonella enterica serovar Typhi forming biofilm on gallstones
  • Proteus mirabilis, Providencia stuartii, P. aeruginosa, and Klebsiella pneumoniae colonizing urinary catheters
  • Legionella pneumophila and Hartmannella vermiformins in potable-water systems
  • Pseudomonas aeruginosa and iron-oxidizing bacteria in natural aquatic systems
  • Methanotroph bacterium from the Methyloglobulus genus in canals
• Characteristics of biofilms


  • Assemblage of microbial cells attached to a substrate and enclosed in a matrix of aggregate materials
  • Cells exhibit unique metabolic functionality, such as antibiotic resistance and production of unique metabolites
• Physical Features of Biofilms


  • Community of cells in close proximity
  • Adhesion/attachment of cells to a biotic or abiotic surface
  • Aggregates encased in a self-produced or externally provided matrix

  
• Size of biofilms


  Broad size range in infections ranging from large multicellular aggregates to small clusters of only a few µm in diameter
• Biofilm matrix


  Extracellular matrix composed of water and extracellular polymeric substances (EPS), primarily polysaccharides, proteins and DNA
• Aggregation and adhesion of biofilms


  • Attached (biofilms formed on a biotic or abiotic surface)
  • Non-attached (detached aggregation not fixed to a surface)

  
• Adaptations of bacteria in biofilms


  • Antimicrobial resistance
  • Quorum sensing
• Biofilms pose a threat to human health as they increase the tolerance of bacterial cells to antibiotics and other antimicrobial agents

  
• Quorum sensing enables colonization of microbial growth in structures which causes damage in marine biofilms

  
• Division of labor in biofilms


  • Emergence of distinct subgroups of genetically identical microorganisms displaying varied behaviors and metabolic functions
  • Allows the community to allocate tasks effectively, promoting maximum efficiency and collaboration
• Biofilm bacteria can exhibit distinct antibiotic tolerance mechanisms compared to planktonic cells
• Persisters, dormant within biofilms, contribute to antibiotic failure and relapse due to reduced metabolism and stress responses
• Biofilm's multicellular nature creates microenvironments that enhance tolerance to antimicrobials

  
• Role of microorganisms in biofilms

  • Nutrient cycling and recycling within the matrix, supporting the growth of microorganisms within the community
  • Degradation of organic compounds allows the release of nutrients such as nitrogen, phosphorus, and sulfur back to the environment (mineralization)
• Biofilms found in microplastics accelerate ammonia and nitrite oxidation and denitrification
• Disintegration of mature biofilms releases nitrogen and phosphorus back into the environment
• Biofilm


  • Multicellular nature
  • Creates microenvironments that enhance tolerance to antimicrobials

  
• Biofilms play an important role in nutrient cycling and recycling within the matrix, supporting the growth of microorganisms within the community