Microbial Environments and Biofilms

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Microbial Environments and Biofilms
2011-12-09 03:17:31
PMB 112 midterm3

general microbiology midterm 3
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  1. microenvironments
    • resources and physiochemical conditions determine growth of microorganisms in an environment
    • growth rate is dependent on the microenvironment
  2. niche
    for a particular organism is defined by the type and quantity of resources and its physiochemical coniditions
  3. prime niche
    habitat in which the organism is most successful
  4. biofilms
    microcolonies of bacterial cells attached to a surface and encased in adhesive polysaccharides excreted by the cells
  5. biofilm structure
    • depends on flow rate
    • low shear - mushrooms
    • higher shear - streamers and ripples
    • contains channels
    • heterogeneous - growth rate, sensitivity to antibiotic, metabolic activity
  6. *biofilm formation and development

    • attachment - adhesion of a few cells to a solid suitable surface
    • colonization - intercellular communication, growth and polysaccharide formation
    • development - more growth and polysaccharide
    • dispersal
  7. in vitro assay for biofilm formation
    • microtiter dishes
    • inoculate wells with bacteria with growth medium
    • wells are stained with crystal violet to stain just the bacteria
    • rinse and see biofilm ring
    • dye can be solubilized in ethanol
    • can be used to isolate mutants defective in biofilm formation
  8. Type IV pili and biofilm formation
    • important for formation
    • *pilA mutant - defective in attachment and biofilm formation
    • pili mediate twitching behavior - facilitate attachment
  9. *autoinducers
    • important for biofilm formation
    • small molecules that allow bacteria to communicate with each other (act as population counters or quorum sensors)
    • once enough bacteria, autoinducers then control expression of genes involved in biofilm formation
    • *intercellular
  10. *cyclic dimeric guanosine monophosphate (c-di-GMP)
    • *intracellular second messenger
    • controls transition to biofilm formation
    • depending on species:
    • 1. attachment via adhesin
    • 2. decreases flagellar motility and increases extra polysaccharide production

    autoinducer (intercellular communication) -> c-di-GMP (intracellular second messenger) -> decreased flagellar motility, increased extra polysaccharide production -> biofilm formation

    GTP (diguanylate cyclases) -> c-di-GMP (phosphodiesterases) -> pGpG ->GMP
  11. dental plaque
    • mixed biofilm
    • 1. saliva provides glycoprotein film for attachment of bacteria
    • 2. colonizationm by streptococcus species
    • 3. then filamentous fusobacterium grow
    • 4. then spirochetes, gram-positive rods, and gram-negative cocci
    • 5. if very heavy plaque, obligate anaerobes may predominate
  12. Why do bacteria form biofilms?
    • defense against: being swept away, phagocytosis by cells of immune system, toxic molecules such as antibiotics
    • biofilms allow cells to remain in a favorable niche
    • biofilms allow bacterial cells to live in close association (single species of mixed communities)
    • may be the typical manner in which bacteria grow in nature where nutrients are typically limiting and there are diverse environmental exposures