Microbial communication

Question 1

what factors were the cause of the accumulation of so much biofilm in the Walkerton water system?

Answer 1

• available water (moisture)
• nutrients ( concrete pipes)
• surface

Question 2

using what you know about regulation of the Iac operon, and what you know about quorum sensing. make a diagram suggesting a method for regulation of an operon regulated by quorum sensing

Answer 2

• inducible operon
• concentration within environment regulates gene expression
• regulators must interact with the components produced by cell

Question 3

why do we study communication within a biofilm?

Answer 3

• to understand

- inhibit biofilm growth by interrupting communication

Question 4

natural competence

Answer 4

uptake of DNA found in environment

• increase possibility for horizontal gene transfers
• uptake for a source of protein

Question 5

are humans prone to a form of unknown signalling similar to quorum sensing (i.e., a response generated due to our environment)?

Answer 5

• pheromones :

Question 6

bacterial pheromones

Answer 6

-all lipid and tend to be gram -

-

Question 7

what is the function of luxR dimer

Answer 7

-it is an enhancer for the operon and allows RNA pol to bind (transcription) and in turn increase AHL productions and compounds leading to luminescence

Question 8

Quorum Sensing

Answer 8

The regulation of gene expression in response to fluctuations in cell population density

Produce and release signal molecules into the environment called autoinducers

Question 9

Pheromones

Answer 9

chemicals capable of acting outside the body of the secreting individual to impact the behaviour of the receiving individual. It is usually the case that we are not aware of the pheromone, it simply triggers a response

Question 10

Vibrio fischeri (squid)

Answer 10

• lux operon ( Intra-species) vibrio fischeri inside squids
  1. ) low levels of cell density and AHL results in no glow.
  2. ) increased level of cells and therefor increased AHL levels
  3. ) AHL levels high enough for dimer formation
  4. ) dimers will activate lux promoter and in turn transcribe +translates operon and proteins
  5. ) translated proteins create luminescence.

Question 11

Rhizobium bac Infection (Root Hair)

Answer 11

• Inter-kingdom (mutualistic relationship )
  1. Plant secretes flavonoids and attract Rhizobium bac
  2. bac create Biofilm cap
  3. Infection of thread (bac proliferation after nod gene expression)–> actin depolymerisation
  4. infection grows into root cortex
  5. infected threads release bac cells –> bacteroids (no cell wall at this point) into root cells
  6. Bacterial cytokinins lead to nodule development + plant cortical cells to divide
  7. plant supplies nutrients and O2 for bacteroids

Question 12

Agrobacterium tumifaciens

Answer 12

• soil borne plant pathogen
• cause infectious crown gall disease
• genes for infection are vir genes on Ti plasmid ( infectious viral DNA)
  1. ) virus enters host via wounds ( virA and virG attracted by acetosyringione)
  2. ) DNA incorporated and leads to auxin and cytokinin and opines productions

Question 13

Auxins

Answer 13

– major role in coordination of many growth and behavioral processes in the plant’s life cycle and are essential for plant body development

Question 14

Cytokinin

Answer 14

plant growth regulators

Question 15

Opines

Answer 15

food source for bac specific to Agrobacterium so it has a selective advantage

Question 16

A.tumifaciens maintain is plasmid during plant infections (quorum sensing)

Answer 16

1. tra genes transfer Ti plasmid into bac (if it is lost)
2. Tra/Tral is regualred by quorum sensing
3. opines inhibit AccR –> transcription
4. TraR produced only if opines around
5. TraR recognize AHL + activate conjugation

Question 17

Inter-species cross talk

Answer 17

• demonstration of cross-talk b/n rhizosphere bac
• -> rhizosphere produce three pigmented antibiotics/phenazines
• phenazine prodcution is reg. by quorum sensing
• phenazine production is reg by PhzR/PhzI systems
• -> I procudes AHL and R is a transcriptional reg.

Question 18

Positive Crosstalk

Answer 18

• mutant bac regain phenazone production ability via AHL signals

Question 19

Negative Crosstalk

Answer 19

• bac inhibit wild type bac to produce phenzaine production via diffusible signals

Question 20

Gram positive bac

Answer 20

• do not have classical AHL mediated quorum
• use gamma-butyrolactones to regulate genes ( resemble AHL somewhat)
• use small peptides and act by de-repressing gene expression
• -> respond Al-2
• two component sensing system+ Autoinducidble peptide= three component system

Question 21

Two component system

Answer 21

1. sensor protein (within cell membrane and senses changes in external envir.) –> communicates with RR (via phosphorylation-dephosphorylation reactions)
2. response-reg (RR) (regulate expression of key genes to respond to external stimulus)

Question 22

Staphylococcus aureus

Answer 22

• three component system

- positive and negative regulation

Question 23

Emergent phenomena within Biofilm

Answer 23

• bac in communities use to enhance their survival (and their community)
• behavior at a larger scale arises from the detailed structure
• exterio cells are exposed first to chemical and antibiotic attacks + first exposed to nutrients
• periphery growth is limited so nutrients can be used for the inner cells as well
• keeping the inner cells alive and well ther biofilm as a whole will better survive an antibiotic treatment.