Microbial Environments and Biofilms

• resources and physiochemical conditions determine growth of microorganisms in an environment
• growth rate is dependent on the microenvironment

for a particular organism is defined by the type and quantity of resources and its physiochemical coniditions

habitat in which the organism is most successful

microcolonies of bacterial cells attached to a surface and encased in adhesive polysaccharides excreted by the cells

• depends on flow rate
• low shear - mushrooms
• higher shear - streamers and ripples
• contains channels
• heterogeneous - growth rate, sensitivity to antibiotic, metabolic activity

• attachment - adhesion of a few cells to a solid suitable surface
• colonization - intercellular communication, growth and polysaccharide formation
• development - more growth and polysaccharide
• dispersal

• 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

• important for formation
• *pilA mutant - defective in attachment and biofilm formation
• pili mediate twitching behavior - facilitate attachment

• 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

• *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

• 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

• 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