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Lecture 17: Biofilms & Motility
Objectives
• Describe the different lifestyles of bacteria.• Describe the three types of bacterial biofilm, and
the five stages of complex biofilm development.• What is signaling used for? How are signaling
molecules and antibiotics related?• What are the different ways that microbes move
and orient themselves?• How do bacteria use solid substrates?• What do the spirochetes and bacteroids have in
common?
Biofilms
Fig. 21.1 Three models of biofilm structure: (A) a monolayer comprising single cells of one species, (B) a stratified biofilm with multiple species, and (C) a three-dimensionally complex biofilm with channels and mushroom structures.
Complex biofilm formation
Extracellular polysaccharides (EPS)
Diatom-produced EPS stabilizes sediments
Complex biofilms: oral biofilms are highly ordered
Biofilm cycles
Fig. 21.2 Biofilm formation cycle by which a freely swimming planktonic cell colonizes a surface and progresses through biofilm formation; capsule and biofilm matrix material depicted in light gray around cells and adherent biomass.
Biofilms are not always static
Staphylococcus aureus (phylum Firmicutes) is an opportunistic pathogen that can also colonize medical devices. It is not always pathogenic, but it is a common cause of skin infections (e.g. boils), respiratory disease (e.g. sinusitis), and food poisoning, complicating infections by often producing proteinaceous toxins. Evil cousin is MRSA. This is an 11 hour time lapse, rolling caused by continuous detachment and reattachment in the direction of flow of the media.
Bacterial lifestyles
• Biofilms• Planktonic growth• Filaments• Aggregates• Layers across gradients• At boundaries, e.g., at air-liquid interfaces called
pellicles or microbial mats• Stalked cells & swarmer cells, as for Caulobacter
crescentis (above)
Pop Quiz!
What is the function of biofilms?a. reserve C sourceb. attachmentc. protection from antibioticsd. protection from desiccatione. all of the above
What are the five stages of complex biofilm development?(1) Initial attachment, (2) Irreversible attachment, (3) Maturation, (4) Recruitment, and (5) Dispersion
Quorum sensing
Different QS signals for different phases of growth, e.g., Pseudomonas aeruginosa
Antibiotics as signals
Shank & Kolter Curr Op Micro 2009
Interspecies Interactions Stimulate Diversification of the Streptomyces coelicolor Secreted Metabolome
Movement & Orientation
• Flagellar movement– Chemotaxis– Spirochaetes
• Non-flagellar movement– Gliding motility, Flavobacteria– Adventurous motility– Magnetosomes– Gas vesicles
Bacterial flagella
Jarrell et al Nat Rev Micro 2008
Archaeal flagella
Flagellar arrangementsA. Monotrichous bacteria have a single
flagellum (e.g., Vibrio cholerae).B. Lophotrichous bacteria have multiple
flagella located at the same spot on the bacteria's surfaces which act in concert to drive the bacteria in a single direction.
C. Amphitrichous bacteria have a single flagellum on each of two opposite ends (only one flagellum operates at a time, allowing the bacteria to reverse course rapidly by switching which flagellum is active).
D. Peritrichous bacteria have flagella projecting in all directions (e.g., E. coli).
Phylum Spirochetes• Phylum Spirochaetae– Class Spirochetes
• Heterotrophic and tend to be microaerophilic or anaerobic
• Saccharolytic (degrade sugar polymers
• Have polar flagella that do not emerge from the outer membrane of the cell
• Corkscrew movement, provides propulsive force
Movement & Orientation
• Flagellar movement– Chemotaxis– Spirochaetes
• Non-flagellar movement– Gliding motility, Flavobacteria– Adventurous motility– Magnetosomes– Gas vesicles
Spirochetes and bacteroids
Phylum Bacteroidetes
• Classes Bacteroidia, Flavobacteria, Sphingobacteria
• Generally saccharolytic anaerobes (bacteroids) or aerobes (flavobacteria, sphingobacteria)
Gliding motility in Flavobacterium
• Flavobacterium gliding is thought to be powered by motors composed of Gld proteins in the cell envelope that propel adhesins, such as SprB, along the cell surface.
Gliding motility in Mycoplasma
Gliding motility: centipede model (L) and inchworm model (R)
Adventurous motility in Myxococcus
Magnetosomes
Magnetotactic motility
Gas vesicles
• Chromatium okenii is a microaerobic sulfide oxidizer that adjusts its buoyance with gas vesicles
Objectives
• Describe the different lifestyles of bacteria.• Describe the three types of bacterial biofilm, and
the five stages of complex biofilm development.• What is signaling used for? How are signaling
molecules and antibiotics related?• What are the different ways that microbes move
and orient themselves?• How do bacteria use solid substrates?• What do the spirochetes and bacteroids have in
common?
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