Strain-Dependent Variation of 18S rDNA Copy Number in Aspergillus fumigatus

Author:

Herrera ML, Vallor AC, Gelfond JA, Patterson TF, Wickes BL

Date: 8 May 2009

Abstract:

Enumerating Aspergillus fumigatus colony forming units (CFU) can be challenging since CFU determination by plate count can be difficult. CFU determination by quantitative real time PCR (qPCR), however, is becoming increasingly common and usually relies on detecting one of the subunits of the multicopy ribosomal RNA genes. This study was undertaken to determine if rDNA copy number was constant or variable among different A. fumigatus isolates. FKS1 was used as a single copy control gene, and was validated against single copy (pyrG and ARG4) and multi copy (arsC) controls. Copy number of the 18S rDNA subunit was then determined for a variety of isolates and was found to vary with strain, from 38-91 copies per genome. Investigation of the stability of 18S rDNA copy number after exposure to a number of different environmental and growth conditions, revealed that the copy number was stable, varying less than one copy across all conditions including isolates recovered from an animal model. These results suggest that while the ribosomal genes are excellent targets for enumeration by qPCR, the copy number should be determined prior to using them as targets for quantitative analysis.

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