How does the phylogenetic species concept correlate with biological characteristics of the pathogenic species in Aspergillus section Fumigati?

Ref ID: 19609

Author:

JA Sugui1*, SW Peterson2, A Figat1, E Mellado3, M Cuenca-Estrella3, KJ Kwon-Chung1

Author address:

1Laboratory of Clinical Infectious Diseases, National Institute of Allergy and Infectious Diseases/NIH,
Bethesda, US
2National Center for Agricultural Utilization Research, Department of Agriculture, Peoria, US
3Centro Nacional de Microbiologí­a, M

Full conference title:

6th Advances Against Aspergillosis 2014

Abstract:

Purpose:
Aspergillus section Fumigati contains twelve clinically relevant species. Among those species
A. fumigatus is the most frequent agent of invasive aspergillosis followed by A. lentulus and
A. viridinutans. Prior phenotypic and phylogenetic analysis concluded that they are separate species,
with A. lentulus more closely related to A. fumigatus than it is to A. viridinutans. Since these three
species are heterothallic, we aimed to find how phylogenetic distance correlates with biological
relatedness judged by their ability of interbreed.
Methods:
Strains tested were clinical and environmental isolates of A. lentulus, A. viridinutans and,
A. fumigatus and four indeterminate clinical isolates (Aspergillus unsp.) from the section Fumigati.
Phylogenetic analyses were carried out with the sequences of ITS, benA, RPB2, Tsr1 and Mcm7.
Thermotolerance was tested on malt extract agar at 25, 30, 37 and 42oC. Antifungal susceptibility
was assayed according to the CLSI M38-A2. Virulence was tested on larvae of Galleria mellonella,
mice immunosuppressed with hydrocortisone and mice with chronic granulomatous disease (CGD).
Mice were inoculated via post-pharyngeal method. Mating crosses were arranged pairwise with
strains of opposite mating type on oatmeal agar and incubated at 30oC.
Results:
Phylogenetic analysis confirmed A. fumigatus, A. lentulus and A. viridinutans are phylogenetically
distinct and also showed that the Aspergillus unsp. isolates form an independent clade, apart from the
other three Aspergilli. All isolates were able to grow at temperatures ranging from 25 to 42oC except
A. viridinutans, whose maximum growth temperature was 37oC. Highest resistance to amphotericin
B, itraconazole and voriconazole was found among the Aspergillus unsp. isolates followed by
A. lentulus, A. fumigatus and A. viridinutans in decreasing order. Virulence assays in larvae of
G. mellonella and CGD mice showed that A. lentulus and A. viridinutans were less virulent than
A. fumigatus. Among the four Aspergillus unsp. strains, two were more virulent than A. fumigatus
in G. mellonella. In CGD mice, however, all four were avirulent. Assays in non-neutropenic balbC
mice immunosuppressed with hydrocortisone revealed that all species, except for A. viridinutans,
were equally virulent. Mating was not observed for A. fumigatus x A. viridinutans, A. fumigatus x
A. lentulus or A. lentulus x A. viridinutans. The complete sexual cycle was only observed in a cross
between one of the Aspergillus unsp. strains (strain labeled as ASP1) with A. fumigatus and in ASP1
x A. viridinutans. SEM morphology of the ascospores produced by ASP1 x A. fumigatus was clearly
distinct from the ascospore morphology produced by mating between A. fumigatus isolates.
Conclusion:
Inter-species mating between A. fumigatus and ASP1 (which is phylogenetically more distant from
A. fumigatus than A. lentulus) suggests that ASP1 is biologically close enough to A. fumigatus
to produce hybrid progeny when mating type incompatibility can be overcome. Our findings
underscore the importance of weighing both genetics and biology in understanding each taxon. It
will be interesting to know whether the inter-species F1 hybrids created in the ASP1 x A. fumigatus
cross are fertile. The analyses with these hybrids are in progress.

Abstract Number: 134

Conference Year: 2014

Link to conference website: http://www.AAA2014.org

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