Aspergillus fumigatus: Growth and Virulence

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Aspergillus fumigatusGrowth and Virulence

• Judith C. Rhodes, Ph.D.
• University of Cincinnati
• Cincinnati, OH, USA
• judith.rhodes_at_uc.edu

2
Aspergillus fumigatus

• Ubiquitous organism.
• Most commonly reported opportunistic hyphomycete.
• Important in compost cycle.
• How did this grass eater become an opportunistic
  pathogen?

3
A. fumigatus Compost to Man

• Life is very competitive in a compost pile.
• What are some of the growth characteristics that
  enable A. fumigatus to be successful in the
  environment that may also allow it to be an
  opportunistic pathogen?

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Growth Traits and Increased Competitiveness

• Thermotolerance Ability to thrive at 37C.
• Germination efficiency
• Growth rate
• Nutritional versatility Ability to sense and
  utilize nutrients in different forms and from
  difference sources.
• Carbon
• Nitrogen

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Germination at 37C

• Three most common pathogens in Aspergillus
  fumigatus, flavus, niger.
• Prevalence as pathogens correlates with
  germination rate at 37C.

Araujo Rodrigues. 2004. J Clin Microbiol
424335.
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Germination Rate

• Correlation is specific to temperature,
  germination rate at elevated temperature is what
  correlates with prevalence.
• Organism must germinate efficiently at body
  temperature to have the opportunity to be a
  mammalian pathogen.

Araujo Rodrigues. 2004. J Clin Microbiol
424335.
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Growth Rate Methods

• Radial growth.
• Biomass.
• Turbidity.
• Dry weight.
• Not all methods give the same answers.

TOTAL 1 x104 CONIDIA
MEASURE DIAMETER AT 24 AND 48 HOURS
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RasB Radial growth/Biomass and Virulence
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Biomass (turbidity) and Virulence
Paisley, et al. 2005. Med Mycol 43397.
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CgrA 37C Radial Growth
Bhabhra, et al. 2004. Infect Immun 724731.
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CgrA Virulence
Flies
Mice
Bhabhra, et al. 2004. Infect Immun 724731.
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ThtA gt37C Growth Virulence
thtA-
Chang, et al. 2004. Fung Genet Biol 41888.
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Thermotolerance

• To be a mammalian pathogen, efficient germination
  and good growth at 37C are required, but high
  temperature growth, gt42C may not be.

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Nutritional Versatility Compost to Man

• A. fumigatus plays a key role in recycling C and
  N in compost.
• Carbon sensing and utilization pkaR and sakA.
• Nitrogen sensing and utilization rhbA, areA,
  cpcA, sakA.
• Auxotrophies pabaA, pyrG, lysF.

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PKA Carbon Signaling and Growth

• In S. cerevisiae, mutants with hyperactive
  cAMP/PKA signaling are unable to utilize
  non-fermentable carbon sources.
• In A. fumigatus, ?pkaR mutants are more growth
  impaired on glycerol, than on glucose.
• In A. fumigatus, PKA activity is high in the
  presence of glucose, but low in the presence of
  glycerol.
• Addition of cAMP to glycerol grown cultures of A.
  fumigatus results in increased PKA activity.

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Carbon Signaling Regulation of alcA
Ethanol
Glucose
creA
creA
A
A
C
C
alcA
alcR
alcR
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PkaR C Sensing and Signaling

• In the wild type, alcA message is induced over
  10-fold in response to ethanol, whereas in the
  DpkaR strain, alcA message was unchanged.
• The lack of alcA induction may indicate that
  carbon catabolite repression is constitutively
  engaged in the DpkaR strain.
• Carbon sensing and/or signaling is perturbed in
  ?pkaR mutant.

Ethanol
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PkaR Virulence
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RhbA Sensing Nitrogen Quality

• RhbA functions upstream in the TOR growth and
  nutrient sensing pathway.
• RhbA responds to N quality and quantity.

plt0.05, plt0.01
Panepinto, et al. 2003. Infect Immun 712819.
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Regulation of rhbA Nitrogen quantity
In vivo 24 h In vivo 72 h In vitro 24 h
rhbA 32.2 9.6 79.7 22.5 11.5 4.2
Zhang, et al. 2005. Mycopathologia 160201.
Panepinto, et al. 2002. Fung Genet Biol 36207.
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RhbA Virulence

• Virulence data and in vivo expression data
  combine to suggest that high quality N is not
  readily available in the host.
• Counter-intuitive.

Panepinto, et al. 2003. Infect Immun 712819.
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Auxotrophies and virulence

• Numerous auxotropies have been shown to decrease
  virulence in A. fumigatus.
• Suggests that some nutritional elements are in
  short supply in the host.

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LysF Growth and Virulence
?lysF
?lysF
Liebman, et al. 2004. Arch. Microbiol. 181378.
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PabaA Virulence
PABA stopped
Brown, et al. 2000. Mol Microbiol 364731.
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How Did a Grass Eater Become an Opportunistic
Pathogen?

• Living in a compost pile translated into the
  ability to
• Germinate and grow efficiently at 37C, i.e.,
  thermotolerance.
• Sense and utilize a variety of carbon and
  nitrogen sources.
• Make its own building block when necessary.
• Make many conidia to compete in a hostile
  environment.
• Sometimes what makes a good grass eater can also
  make a good opportunistic pathogen.

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Acknowledgements

• Brian Oliver
• John Panepinto
• Jarrod Fortwendel
• Wei Zhao
• Tom Amlung
• Darcey Smith
• Amy Seitz
• Lauren Fox

• David Askew
• Doug Boettner
• Ruchi Bhabhra
• Mike Miley
• NIAID