Pathogens as Prey

1
Pathogens as Prey
2
Predators of bacteria

• Some nematodes, earthworms (soil)
• Amoeba, other protozoa (s,w)
• Myxococcus (s)
• Bdellvibrio BALO (water)
• Phages (s, w)

www.soilandhealth.org/.../ ingam/ingham.html
www.vet.upenn.edu/.../ 55/bacteriophage.html
3
Bdellvibrio bacteriovorus

• Bdellovibrio bacteriovorus
• gram negative curved rod
• 0.3 um in width and 1 to 2 um in length
• Present in all environments
• obligate aerobe
• Optimal growth at 28-30 C
• Large genome (3.85M bp)
• Distinct attack phase

http//www.bbc.co.uk/radio4/science/thematerialwor
ld_20051013.shtml

• http//web.umr.edu/microbio/BIO221_2001/bdellovib
  rio_bacteriovorus.html

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Prey

• Gram negative bacteria
• The periplasm is the volume between the inner and
  outer membranes
• Gram-negative bacteria digest nutrients in the
  periplasm prior to the transport of the nutrients
  into the cytoplasm
• Bdellovibrio dependent on prey to complete
  lifecycle
• Can attack biofilms
• Often studied attacking E. coli or Pseudomonas

http//www.dartmouth.edu/gotoole/Bdellovibrio.htm

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Bdellovibrio life cycle

• 1 3 hours
• Can go dormant during bdelloplast stage

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On the Hunt

• Attack state highly mobile and can not
  reproduce
• Moves very fast 160 um/s (human moving 4 mph)
• Chemotaxis - chemical sensing to find target
  rich environments

Bdellovibrio attached to a cell of
Pseudomonas http//www.micro-gen.ouhsc.edu/b_bacte
r/b_bacter_home.htm
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Chemotaxis

• Bdellovibrio genome contains 18 known chemotaxis
  genes and 1 known aerotaxis genes
• At least one gene shown to directly contribute to
  predation efficiency
• Actual chemical molecules and signals used are
  unknown
• Chemotaxis likely used to find environments
  favorable to prey species
• Quorum sensing signals are not utilized

8
Attacking Prey

• Target of attack on prey outer cell membrane is
  unknown
• No known mechanisms of resistance in prey
• Likely target is either non-specific or highly
  conserved receptor necessary for cell viability
• Subject of intense research as exact target has
  been naturally selected as a favorable strategy
  and may lead to development of novel antibiotics

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Entry and Attachment

• Bdellovibrio uses flagella to make physical
  contact, grabs on with pili
• Attachment is initially reversible, becomes
  permanent after initial recognition step
• May have preferred prey attachment rates differ
  in mixed populations
• Enters through hole induced in outer membrane by
  peptidoglycan hydrolysis

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Formation of the Bdelloplast

• Bdellovibrio restabilizes prey outer membrane to
  contain nutrients and protect against dehydration
• Bdellovibrio attaches to the inner membrane
  causing the cytoplasm to round up into the
  osmotically stable Bdelloplast
• Exact mechanism of Bdelloplast formation is
  unknown but prey membrane maintains structural
  integrity
• Bdellovibrio begins to extract and digest prey
  cellular components

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Prey Utilization

• Nearly all of the prey bacteria is utilized
• Prey components are broken down via hydrolysis
  and used to replicate additional Bdellovibrio or
  metabolized for energy
• About 50 of prey nucleic acid utilized for de
  novo synthesis
• Ribose from other 50 metabolized for energy
• Final rupture of cell wall degrades
  peptidoglycans, liberating sugars and amino acids
  that can be used by Bdellovibrio

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Hydrolysis

• Few prey molecules utilized intact, must break
  down for own biosynthesis
• Large number of genes for hydrolytic enzymes
• Radiolabeling and electrophoresis confirm prey
  molecules are degraded before synthesis

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Synthesis

• Sophisticated coordination by predator regulators
  ensures smooth pathway from degradation to
  synthesis
• Hydrolytic degradation products incorporated into
  ongoing synthesis
• Regulators are unknown
• Bdellovibrio genome contains many synthesis
  genes, including 3 for ATP alone

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Nucleic Acid Synthesis

• Prey nucleic acids initially cuts with
  endonucleases
• Molecules then taken apart one at a time with
  exonucleases
• To replicate offspring, Bdellovibrio must
  synthesize much more nucleic than contained
  within prey
• E.coli prey cell contains 4M bp
• Bdellovibrio produced 4 offspring synthesizes
  approximately 15M bp

15
Protein Synthesis

• Bdelloplast can not replicate full set of amino
  acids
• This suggests Bdellovibrio is only capable of
  protein synthesis with access to prey amino acids

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Reproduction

• of offspring limited by raw material available
  from prey
• As Bdelloplast grows it elongates into a
  filamentous structure containing all replicated
  chromosomes
• As Bdellovibrio senses the prey has become
  exhausted the Bdelloplast is organized and
  septates into the individual progeny
• The remaining prey membrane is lysed and progeny
  are set free

Starr and Baigent,, JOURNAL OF BACTERIOLOGY, May,
1966 Vol. 91, No. 5