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Microbiology BIO-5015B > Lecture 28: Bacterial disease of plants (and animals) > Flashcards

Lecture 28: Bacterial disease of plants (and animals) Flashcards

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1
Q

What are different types of plant pathogenic bacteria?

A 
1. Saprophytes - grow in soil on dead 
   organic matter
2. Epiphytes - grow on external plant 
    surfaces 
3. Pathogens - grow on internal plant 
    surfaces causing disease 
   a. Biotrophs - keep host alive
   b. Necrotrophs - kill host as a way of life
   c. Hemibiotrophs - switch from biotrophy 
       to hemibiotrophy
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2
Q

What are the main genera of bacteria plant diseases? What are these pathogens?

A
  1. Pseudomonas
  2. Xanthomonas
  3. Erwinia
  4. Agrobacterium

These are “facultative pathogens”, I.e:
a. Exist as saprophytes or epiphytes
b. Migrate into plant tissues, replicate,
and cause disease

Disease e.g; fruit rot, wilt, leaf blight, stalk root

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3
Q

How do you identify disease causing bacteria using “Koch’s postulates”?

A
  1. Disease occurs naturally
  2. Isolate and grow in pure culture
  3. Inoculate healthy plant
  4. Development of original disease
  5. Re-isolate bacterium
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4
Q

What are examples of gram negative plant pathogens? what is there name, host range, and disease?

A

Necrotrophic:

  1. Erwinia carotovora
    a. Host range: Wide
    b. Disease: Soft rots

Biotrophic:

  1. Erwinia amylovora
    a. Host: Rosacaeae
    b. Disease: fire blight
  2. Ralstonia solanacearum
    a. Host range: wide
    b. Wilts
  3. Xanthamonas campestris pv. vesicatoria
    a. Host: pepper, tomato
    b. Disease: leaf spot
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5
Q

What is meant by virulence and how can it be measured?

A

Virulence: The severity of an infection

1. Inoculate host (via; syringe infiltration, 
   spraying, or dripping)
2. Allow disease development
3. Take samples
4. Grind in buffer 
5. Make serial dilutions 
6. Plant, incubate, and count colonies

Example: avrRPM1 gene from Pseudomonas syringae pv. maculicola is required for full virulence on Arabidopsis

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6
Q

What is meant by the “type 2 secretion system (T2SS)” in virulence? What is the process and what are the components?

A
  1. T2SS is a two-step process:
    a. SecYEG or Tat system transport
    proteins into periplasm
    b. Dodecameric secretin GspD transports
    proteins across the outer membrane
  2. Four components
    a. Cytoplasmic ATPase (GspE)
    b. IM platform (4 membrane proteins -
    GspC, GspF, GspL, GspM)
    c. Periplasmic pseudopilus (GspG)
    d. OM complex (GspD) aka ‘secretin’

IM = inner membrane
OM = outer membrane
Tat system = twin-arginine translocation
Gsp = general secretion pathway

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7
Q

What does T2SS do for virulence in animal pathogens?

A
  1. Free-living bacteria; T2SS secretes
    enzymes that degrade compounds in the
    environment (incl. proteases, lipases,
    Chitinases)
  2. Pathogens that require T2SS e.g.,
    a. Yersinia enterocolitica yts1E (ATPase-)
    mutants show reduced infection in
    mouse
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8
Q

What does T2SS do for virulence in plant pathogens?

A

T2SS secretion of cell wall degrading enzymes by “necrotrophic” Erwinia species (soft rots). Best studied: E. chrysanthemi and E. carotovora

  1. Pectate lyase, endo- and exo- enzymes (at least 9)
  2. Pectin acetylesterase
  3. Pectin methylesterase (2)
  4. Polygalacturonase
  5. Cellulase (2)
  6. Endoxylanase
  7. Protease (at least 4)
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9
Q

What is the “Type 3 secretion system (T3SS)” in bacterial virulence?

A
  1. T3SS
    a. Multi-protein nano-machine, structurally related to bacterial flagella
    b. Transfers “effector proteins” from bacterium “into host cytoplasm”
  2. Components (in salmonella) include:
    a. Hexameric ATPase (InvC)
    b. Sorting platform (SpaO, OrgA, OrgB)
    c. Secretin (InvG)
    d. Needle (Prgl)
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10
Q

What does T3SS do for virulence in animal pathogens?

A

T3SS required for virulence of some animal/human pathogens.

E.g., Shigella flexneri T3SS effector IpaB
induces apoptosis in macrophages

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11
Q

What does T3SS do for virulence in plant pathogens?

A
  1. Bacterial Hrp proteins form a T3SS
  2. Several Hrp proteins form a pilus
    through which effectors (incl. Avrs) are
    translocated
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12
Q

What are T3 effectors; TALEs?

A 
1. AvrBs3, PthA, AvrXa7, and related 
   proteins from Xanthomonas species 
   make up TALE family
2. TALE: "transcription activator-like 
    effectors"
3. Exhibit sequence specific DNA binding
4. Act as transcriptional activators
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13
Q

What does the TALE “AvrPtoB” do?

A
  1. Suppresses PAMP-triggered immunity
    (PTI)
    a. FLS2 recognition of flagellin
    b. FLS2 binds to flagellin (a protein of
    bacterial flagella)
    c. Binding causes intracellular signalling,
    turning on defence against bacteria
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14
Q

What is type 4 secretion (T4SS) in bacterial virulence?

A
  1. “Ti” plasmid is inserted into plant cell
    target containing “tDNA”, which gets
    incorporated into plant chromosome
  2. EXAMPLE: “Crown Gall”
    a. Caused by Agrobacterium tumefaciens
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15
Q

What genes are contained within the T-DNA of the octopine-type Ti plasmid

A
  1. aux - auxin biosynthesis genes
  2. cyt - isopentyl transferase (involved in
    cytokinin biosynthesis)
  3. tm1 - tumour size regulation
  4. ocs - octopine synthase
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16
Q

What are “Exopolysaccharides” in bacterial virulence?

A
  1. Exopolysaccharides - extracellular
    polysaccharide (EPS)
  2. Form a capsule around most bacterial
    cells
16
Q

What are “Exopolysaccharides” in bacterial virulence?

A
  1. Exopolysaccharides - extracellular
    polysaccharide (EPS)
  2. Form a capsule around most bacterial
    cells
17
Q

What is the virulence function of animal pathogen exopolysaccharides?

A
  1. Req. for virulence of some animal
    pathogens. E.g.,
    a. Klebsiella pneumoniae K antigen
    (capsular polysaccharide)
18
Q

What is the virulence function of plant pathogen exopolysaccharides?

A 
1. e.g., Xanthomonas campestris pv. 
   campestris (Xcc):
2. EPS suppresses Ca2+ signalling, and 
    thus, the expression of plant defence 
    genes like "PR1"
19
Q

What is the virulence function of animal pathogen toxins such as cholera toxin?

A
  1. B subunit of toxin binds to GM1
    gangliosides on surface of gut epithelial
    cells
  2. A subunit is internalised and activates
    adenylate cyclase
  3. increase intracellular cyclic AMP levels
    over activate protein kinase A
  4. PKA phosphorylates cystic fibrosis
    transmembrane conductanse regulator
    (CFTR) causing loss of Cl-, Na+, and
    HCO3- and H2O from the cell
20
Q

What is the virulence function of plant pathogen toxins such as coronatine toxin?

A
  1. coronatine
    a. mimics the plant hormone “jasmonic
    acid”
    b. suppresses stomatal closure (a
    consequence of PTI)

Microbiology BIO-5015B (30 decks)

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