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Microbiology BIO-5015B > Lecture 6: Biofilms > Flashcards

Lecture 6: Biofilms Flashcards

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1
Q

What are biofilms?

A

“Matrix-enclosed bacterial populations adherent to each other and/or to surfaces or interfaces with a self-produced extra-cellular matrix”

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2
Q

How is a biofilm built?

A
  1. Free swimming bacteria
  2. Reversible adsorption on the substratum
  3. Production/secretion of polysaccharide
  4. Maturation of biofilm
  5. bacterial detachment
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3
Q

What are the requirements of biofilms?

A
  1. surface (solid-liquid or gas-liquid interface) - lose flagella once attached to surface
  2. moisture
  3. nutrients
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4
Q

How is a multispecies biofilm built?

A
  1. Primary colonizers (2+ different species nearby)
  2. Cell division of each specie forming growing microcolonies (EPS getting closer)
  3. EPS (matrix bubbles) join, creating a sealed and large environment between the two species
  4. Secondary colonizers ‘coahese’ (secondary colonizers include: single cells, coaggregates, and groups of cells)
  5. Cell division resulting in MATURE MULTI-SPECIES BIOFILM
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5
Q

Give an example of a diverse biofilm in nature (various species).

A

Dental plaque

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6
Q

How do biofilms form in the sea?

A
  1. Bacterial cells settle on hard surface
  2. Cells proliferate and secrete slime = formation of biofilm
  3. Some cells detach
  4. Protists graze on bacteria
  5. If enough biofilm forms, large organisms can attach (e.g, barnacle larva and algal spores)
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7
Q

Where do biofilms form in the sea?

A
  1. Rocky surface

2. The ‘hull’ under a ship

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8
Q

What does EPS stand for? What is it?

A

EPS = Extracellular Polymeric Substance

  • Holds biofilms together
  • Often contains extracellular polysaccharides
  • SOME CELLS within biofilm produce EPS - this acts as glue to generate structures
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9
Q

What can the EPS trap? What does this do?

A

Particulate materials such as: clay, organic materials, dead cells, and precipitated minerals. -this FURTHER INCREASES THE BULK AND DIVERSITY OF THE BIOFILM HABITAT

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10
Q

How do bacterial characteristics vary when in biofilms compared to free-living?

A
  1. Gene expression

2. Co-ordinated behaviour within biofilms, with intercellular communication via signalling molecules

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11
Q

How do biofilms react to antibiotics?

A

Biofilms are less susceptible to antibiotics - even when prolonged for long periods of time some cells will still persist

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12
Q

What are examples of beneficial biofilms?

A
  1. Bioremediation: waste water treatment plants

2. Healthy gut flora

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13
Q

How do biofilms relate to infections?

A
  1. Bacterial Endocarditis (infection of inner surface of heart and its valves)
  2. Cystic Fibrosis
  3. Legionnaires disease (respiratory infection resulting from aspiration of clumps of LEGIONNELLA biofilms detached from air and water heating/cooling distribution systems)
  4. HIGHLY RESISTANT TO ANTIBIOTICS
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14
Q

What strategies can be used to prevent biofilms formation?

A
  1. Coat surface
  2. Novel antibiotics early on
  3. Dissolution of biofilm matric
  4. Deliver signal blockers
  5. Induce detachment
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15
Q

What is the definition of Quorum Sensing and what is it?

A

Definition: “Regulation of gene expression in response to fluctuation in population density”

  • A form of bacterial communication allowing the ability of bactiera to count their numbers
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16
Q

Give an example where quorum sensing can be seen. Explain what happens

A

Vibrio fischeri.

  • gram negative bacterium
  • lives in light sensing organs of bobtail squid which relies on the bacteria to calculate the moon light shining above and emit the same amount downward (STOP SQUID BEING SEEN FROM BELOW)
17
Q

How does the bobtail squid prevent over population of V fischeri?

A

Eviction of all bacteria every dawn. Bacteria recolonize during the days creating a fresh quorum.

18
Q

What are the two key components of light emission of Vibrio fischeri during quorum sensing? what do they do?

A
  1. Luxl - produces the signal molecule (often called autoinducer, Al)
  2. LuxR - transcriptional activator

Upon binding Al, LuxR activates a set of genes including the ‘lux’ genes for bioluminescence -Lucl then produces more Al

COMMON MECHANISM FOR GRAM - BAC

19
Q

What is the two component signal transduction system in bacteria?

A
  • It is important for signalling in gram-positive bacteria

- Sensor His Kinase -> Response regulator

20
Q

What is oligopeptide mediated quorum sensing? What bacteria does it occur in? What are the components and what do they do?

A
  1. Occurs in gram-positive bacteria
  2. Two (/three) components
    a. H: His of a sensor kinase
    b. D: Aspartate of the response regulator
    c. (ABC Transporter: for secretion of
    the signalling molecule)
21
Q

What happens in oligopeptide mediated quorum sensing?

A
  1. specific precursor molecule produced
  2. this is modified, processed , and secreted by ABC transporter (oligopeptide now called OLIGOPEPTIDE AUTOINDUCER)
  3. oligopeptide inducer accumulates as cells grow
  4. At high cell density, autoinducer is detected by 2 component transduction system
  5. Sensor kinase protein recognises the autoinducer and therefore autophosphorylates at a conserved histidine residue (H)
  6. Phosphoryl group transferred to cognate response regulator protein which is phosphorylated at a conserved aspartate residue (D)
  7. response regulator binds to specific target promoters to modulate expression of quorum sensing regulated genes
22
Q

How do pathogens use quorum sensing?

A
  1. Bacteria quietly grow in number
  2. Population reaches certain level leading to instant changes in:
    a. behaviour
    b. appearance
    c. metabolism
  3. Changes accumulate in an infection - ambushing and potentially overwhelming the immune system
23
Q

How does Pseudomonas aeruginosa use quorum sensing?

What are examples of virulence factors?

A

Uses a hierarchical quorum sensing circuit to regulate expression of virulence factors and biofilm formation.

Virulence factors:

  1. Lipopolysaccharide - endotoxin activity
  2. Pyocyanin - stimulates inflammatory response, mediates tissue damage
  3. Exotoxin A - inhibition of protein synthesis, produces tissue damage
  4. Elastase - destruction of elastin containing tissues
  5. Alkaline protease - Tissue destruction, inactivation of interferon
  6. Rhamnolipid - Heat-stable haemolysin, inhibits pulmonary ciliary activity
24
Q

How are bacteria multilingual?

A

There is a vast array of different molecules used for signalling - bacteria in many cases are able to detect and respond to many

25
Q

Explain bilingual communication in V. harveyi

A
  1. AI-1 molecule - speaks language to V. harveyi

2. AI-2 molecule - speaks universal language used by many quorum sensing bacteria

26
Q

What is the signalling molecule in Gram positive bacteria

A

oligopeptide autoinducers

27
Q

WHat are the signalling molecules in gram-negative bacteria

A

Acyl homoserine lactone autoinducers

Microbiology BIO-5015B (30 decks)

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