Black aspergilli: A remaining challenge in fungal taxonomy? - 16/09/17
Résumé |
Aspergillus section Nigri is a taxonomically difficult, but medically and economically important group. In this study, an update and revision of the taxonomy of A. section Nigri strains within the BCCM/IHEM collection has been conducted. There are currently 26 accepted species within the Nigri section.
The use of Bt2 primers (Bt2a and Bt2b) has been shown to be problematic for the A. section Nigri (Hubka et al., 2012). Bt2 primers can amplify either benA fragments (three introns) or paralogous tubC fragments (two introns) in the Nigri section. When a mix of those two paralogues is used in phylogenies, this can create incongruent trees and possible misidentification of the tested strains. Until recently, the Bt2 primers have been used in the BCCM/IHEM collection to classify A. section Nigri strains. Given the risk of false identifications, we therefore revised the classification of these strains.
A total of 183 strains of the A. section Nigri were molecularly (re-)analyzed. Three regions were amplified [β-tubulin (Ben2f/Bt2b), calmodulin (CF1L/CF4) and ITS (ITS5/ITS4)] and a multilocus phylogeny of the combined loci was created by using maximum likelihood analysis. The Ben2f/Bt2b primer pair was shown to be highly specific for the benA gene (Hubka et al., 2012) and calmodulin has been proposed as a secondary identification marker for Aspergillus species by Samson et al. (2014).
The analysis resulted in 48 reclassifications and name changes. In total, we identified 17 different species of the Nigri section in our collection. The paralogous tubC gene was previously amplified for six BCCM/IHEM strains within the A. aculeatus-clade. The new β-tubulin primer pair used in this study amplified the correct benA gene for these six strains. The majority of the clinical samples were found within A. tubingensis and the A. niger/welwitschiae complex, but also A. brunneoviolaceus, A. neoniger, A. japonicus, A. carbonarius, A. luchuensis, A. piperis and A. vadensis were isolated from clinical samples. We also evaluated the usefulness of MALDI-TOF MS for species identification within the Aspergillus section Nigri of the BCCM/IHEM collection and found that in general, MALDI-TOF MS could discriminate between these closely related species.
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Vol 27 - N° 3
P. e2 - septembre 2017 Retour au numéro
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