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Strain-dependent variation in 18S ribosomal DNA Copy numbers in Aspergillus fumigatus

M L Herrera1, A C Vallor, J A Gelfond

  • 1Department of Microbiology and Immunology, the University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-3900, USA.

Journal of Clinical Microbiology
|March 6, 2009
PubMed

Insights

Enumerating Aspergillus fumigatus using quantitative PCR (qPCR) is common, but ribosomal DNA (rDNA) copy number varies significantly between strains. Researchers found rDNA copy number is stable across conditions, but must be determined per strain for accurate qPCR quantification.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Enumerating Aspergillus fumigatus colony-forming units (CFU) is challenging with traditional plate counts.
  • Quantitative real-time PCR (qPCR) is increasingly used for CFU determination, often targeting multicopy rRNA genes.
  • The variability of ribosomal DNA (rDNA) copy number in A. fumigatus isolates is not well-established.

Purpose of the Study:

  • To investigate the variability of ribosomal DNA (rDNA) copy number among different Aspergillus fumigatus isolates.
  • To assess the stability of rDNA copy number under various environmental and growth conditions.
  • To provide guidance for accurate qPCR-based enumeration of A. fumigatus.

Main Methods:

  • Validated single-copy control genes (FKS1, pyrG, ARG4) against multicopy controls (arsC).
  • Determined 18S rDNA copy number in various A. fumigatus isolates using qPCR.
  • Assessed the stability of 18S rDNA copy number after exposure to diverse conditions, including an animal model.

Main Results:

  • Ribosomal DNA (rDNA) copy number varied significantly among A. fumigatus strains, ranging from 38 to 91 copies per genome.
  • The 18S rDNA copy number remained stable across different environmental and growth conditions, including isolates from an animal model.
  • Copy number variation was less than one copy across all tested conditions.

Conclusions:

  • Ribosomal genes are suitable targets for qPCR-based enumeration of Aspergillus fumigatus.
  • The copy number of target ribosomal genes must be determined for each specific isolate prior to quantitative analysis.
  • Accurate qPCR quantification of A. fumigatus requires strain-specific validation of rDNA copy number.

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