What is the difference between a bacterium and a bacterial biofilm?

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The other day, I overheard someone in the lab wondering why some bacterial infections are so stubborn and hard to treat, and it reminded me of something I had read in a microbiology paper. It turns out that the way bacteria live—whether as individual cells or in a biofilm—makes a huge difference. Here’s a detailed explanation of how planktonic bacteria differ from bacterial biofilms in terms of structure, behavior, and resistance.

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Anttilampinen 2025-06-13T18:53:40+00:00 1 Answer 2 views
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  1. fleming
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    2025-06-13T18:56:59+00:00
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    Definition and Basic Nature

    • Bacterium (Planktonic Cell): A single, free-floating bacterial cell living independently. This is the traditional way bacteria have been studied in laboratory cultures.
    • Bacterial Biofilm: A complex, three-dimensional community of bacteria (often multiple species) embedded in a self-produced matrix of extracellular polymeric substances (EPS). Biofilms attach to surfaces and to each other, forming structured communities with coordinated behaviors.

    Structure and Composition

    • Bacterium (Planktonic Cell):
      • A discrete, individual cell with defined boundaries
      • Typically surrounded by a cell membrane and cell wall
      • Contains cytoplasm, ribosomes, nucleoid, etc.
      • May possess flagella for motility
    • Bacterial Biofilm:
      • A complex architecture with multiple layers and channels
      • Composed of many bacterial cells (often billions) possibly from multiple species
      • Embedded in a matrix (70–95% of biofilm volume) made of:
        • Extracellular polysaccharides
        • Proteins
        • Extracellular DNA (eDNA)
        • Lipids
        • Water channels for nutrient and waste flow
      • Distinct microenvironments with different oxygen levels, pH, and nutrients
      • May include structures like mushroom-shaped towers or streamers

    Formation and Development

    • Bacterium (Planktonic Cell): Reproduces via binary fission and maintains uniform characteristics.
    • Bacterial Biofilm: Develops through stages:
      1. Initial attachment: Reversible attachment to a surface
      2. Irreversible attachment: Cells commit to attachment
      3. Microcolony formation: Cells multiply and produce EPS
      4. Biofilm maturation: Develops complex 3D structures
      5. Dispersion: Release of cells to colonize new surfaces

      Development is regulated by quorum sensing (cell-to-cell communication).

    Gene Expression and Phenotype

    • Bacterium (Planktonic Cell): Uniform gene expression; optimized for individual survival.
    • Bacterial Biofilm:
      • Up to 40% different gene expression compared to planktonic cells
      • Heterogeneous phenotypes within the biofilm
      • Biofilm-specific genes for adhesion, EPS production, stress response
      • Reduced metabolic activity in deeper layers

    Resistance Properties

    • Bacterium (Planktonic Cell):
      • More susceptible to antibiotics, disinfectants, and immune defenses
      • Uniform susceptibility across population
    • Bacterial Biofilm:
      • 10–1000 times more resistant to antimicrobials
      • Resistance mechanisms include:
        • EPS matrix as a physical barrier
        • Slow-growing/dormant interior cells
        • Biofilm-specific resistance genes
        • Persister cells
        • Enzymatic degradation of antimicrobials
        • Heterogeneous susceptibility across biofilm

    Metabolic State

    • Bacterium (Planktonic Cell): Generally metabolically active with uniform metabolic states.
    • Bacterial Biofilm:
      • Metabolic stratification:
        • Surface: Active metabolism
        • Interior: Dormant or slow-growing
      • Oxygen and nutrient gradients create different zones
      • Cooperation and division of labor among cells

    Communication and Coordination

    • Bacterium (Planktonic Cell): Limited communication, acts independently.
    • Bacterial Biofilm:
      • Uses quorum sensing for cell-to-cell communication
      • Coordinates:
        • Gene expression
        • Metabolic division of labor
        • Stress responses
        • Dispersal

    Medical and Industrial Significance

    Medical Implications

    • Planktonic Bacteria: Cause acute infections treatable with standard antibiotics.
    • Biofilms: Linked to chronic, persistent infections such as:
      • Chronic wound infections
      • Implant/device-related infections
      • Cystic fibrosis lung infections
      • Chronic otitis media
      • Dental plaque and gum disease
      • Urinary tract infections

    Industrial Implications

    • Biofilms: Cause:
      • Biofouling of equipment
      • Contamination in food production
      • Microbially influenced corrosion
      • Clogged water systems

    Beneficial Roles

    • Biofilms: Useful in:
      • Wastewater treatment
      • Bioremediation
      • Fermentation (e.g. vinegar production)
      • Natural ecosystems (soil and water)

    Examples

    • Common Biofilm-Forming Bacteria:
      • Pseudomonas aeruginosa – cystic fibrosis lungs
      • Staphylococcus aureus and S. epidermidis – medical devices
      • Escherichia coli – urinary catheters
      • Streptococcus mutans – dental plaque
      • Legionella pneumophila – water systems

    A bacterium is a single, free-living microbial cell, while a bacterial biofilm is a structured, surface-attached community of bacteria in a protective matrix. Biofilms are more resistant to treatments and play roles in both disease and environmental processes. Understanding their behavior helps in controlling infections and utilizing their benefits in industry and nature.

    Sources: Flemming, H.C., et al. (2016). Biofilms: an emergent form of bacterial life. Nature Reviews Microbiology; Costerton, J.W., et al. (1999). Bacterial biofilms: a common cause of persistent infections. Science.

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