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Molecular variability of Pseudallescheria boydii, a neurotropic opportunist
J Rainer1, G S de Hoog, M Wedde
1Centraalbureau voor Schimmelcultures, Baarn, The Netherlands.
Abstract:
The sequences of the internal transcribed spacer (ITS) ribosomal DNA (rDNA) domain data obtained by restriction fragment length polymorphism analysis with 18S rDNA and fingerprinting (M13) for clinical and environmental strains of Pseudallescheria boydii (anamorph, Scedosporium apiospermum) were compared to those for related species of Pseudallescheria, Petriella, and Scedosporium. The infraspecific variability of P. boydii was considerable. There were five different lengths in the 18S rDNAs within P. boydii due to the occurrence of introns. In several cases, strains isolated from a single pond or ditch proved to be genetically very different. Nevertheless, some lineages had a regional distribution. The variability found is unlikely to be explained by meiotic recombination alone. Pseudallescheria fusoidea, Pseudallescheria ellipsoidea, and Pseudallescheria angusta were found to be synonyms for P. boydii. Scedosporium prolificans was found amid Petriella species in the ITS tree and showed no infraspecific variability. The type strain of Rhinocladium lesnei proved to be identical to Graphium putredinis. Acladium castellanii, which is morphologically reminiscent of S. apiospermum, was also found to be a separate species, but with an unknown affiliation.
Insights
Genetic analysis of Pseudallescheria boydii revealed significant infraspecific variability, challenging previous classifications. Several species were identified as synonyms for P. boydii, highlighting complex fungal diversity.
Area of Science:
- Mycology
- Molecular Systematics
- Fungal Genetics
Background:
- Pseudallescheria boydii (anamorph, Scedosporium apiospermum) is a fungus with clinical and environmental relevance.
- Understanding the genetic diversity within P. boydii is crucial for accurate identification and epidemiological studies.
Purpose of the Study:
- To compare the internal transcribed spacer (ITS) ribosomal DNA (rDNA) sequences of P. boydii strains with related species.
- To investigate the infraspecific variability within P. boydii using molecular methods.
Main Methods:
- Restriction fragment length polymorphism (RFLP) analysis of 18S rDNA.
- DNA fingerprinting using the M13 marker.
- Phylogenetic analysis of ITS rDNA sequences.
Main Results:
- Considerable infraspecific variability was observed in P. boydii, with five different 18S rDNA lengths due to introns.
- Genetically distinct strains of P. boydii were isolated from single environmental sources, suggesting complex population structures.
- Pseudallescheria fusoidea, P. ellipsoidea, and P. angusta were identified as synonyms of P. boydii.
- Scedosporium prolificans showed no infraspecific variability and clustered with Petriella species.
- Rhinocladium lesnei was found to be identical to Graphium putredinis.
Conclusions:
- The genetic variability in P. boydii likely exceeds that explained by meiotic recombination alone.
- The study reclassifies several fungal species, clarifying the taxonomy of the Pseudallescheria and Scedosporium genera.
- Acladium castellanii was confirmed as a distinct species with uncertain phylogenetic placement.