Book of Abstracts (PDF) - International Mycological Association

IMC7 Thursday August 15th Lectures
255 - Biogeography of floricolous yeasts: is everything
everywhere?
M.A. Lachance
Department of Biology, University of Western Ontario,
London, Ontario N6A 5B7, Canada. - E-mail:
lachance@uwo.ca
The old dogma of microbial ecology, 'Everything is
everywhere, the environment selects,' has had a profound
influence on the study of yeast biodiversity. One outcome
has been a widespread neglect of the habitat as a significant
element of species descriptions. The traditional paradigm
implies that a global 'yeast seed bank' is available to fill
any niche that is made available. Biogeographic theory, on
the other hand, predicts that species diversity should be
higher in the tropics, lower in isolated localities, and
proportional to the size of contiguous landmasses. To test
these opposing models, the yeast communities of
ephemeral flowers were studied in various Pacific islands
and several sites in Australia, Brazil, Costa Rica, the
southern United States, and the eastern Nearctic region.
These yeasts are vectored and maintained by insects such
as bees and beetles. The yeast species composition is
greatly but not exclusively affected by the nature of the
vector insect species, and much less so by the plant species.
Most biogeographic factors have a significant influence
when not confounded by human interference. Different
yeast species have different ranges on the global scale:
some can be viewed as cosmopolitan and others as
endemic. The emerging pattern is that indeed, the
environment selects. However, geography plays a major
role. The notion that 'everything is everywhere,' as least at
it applies to floricolous ascomycetous yeasts, is misleading.
256 - Molecular ecology of basidiomycetous yeasts in
tropical marine habitats
J.W. Fell
University of Miami, 4600 Rickenbacker Causeway, Key
Biscayne, Fl, U.S.A. - E-mail: jfell@rsmas.miami.edu
The current model of yeast systematics includes ^ 1000
species in >100 genera, numbers that are rapidly increasing
with the discovery of new species and the description of
new genera due to increased knowledge of the biology and
phylogenetics of these unicellular ascomycetous and
basidiomycetous fungi. Estimates indicate that this number
of species may only represent 1% of the species in nature.
Yeasts in marine environments are widespread from the
tropics to polar regions and intertidal habitats to the deep
sea floor. The ecological role of yeasts ranges from species
that are host specific saprophytes to species with diverse
habitats and appetites. Our specific knowledge of these
roles is, however, meager. A major reason has been the
lack of ability to specifically identify these organisms to
the species level. The advent of molecular techniques has
provided the necessary cure to the systematic problems.
82
Book of Abstracts
Research in our laboratory with the basidiomycetous yeasts
has centered on the ribosomal DNA, exploring the ITS,
D1D2 portion at the 5' end of the large subunit, and the IGS
regions. Based on these data bases, the phylogenetic
position and identity of yeasts can be determined. The
sequence differences between strains and species has
spawned methods for the rapid identification of culturable
and uncultured species directly from the environment.
These methods will be discussed.
257 - Systematics of the human pathogen Cryptococcus
neoformans in the genomics era
T. Boekhout 1* , B. Theelen 1 , M. Diaz 2 , J.W. Fell 2 , K.J.
Kwon-Chung 3 , M.T. Barreto de Oliveira 4 , L. Trilles 5 , M.
Lazera 5 , R. Falk 6 , I. Polacheck 6 & W. Meyer 7
1 Centraalbureau voor Schimmelcultures, Uppsalalaan 8,
3584 CT Utrecht, The Netherlands. - 2 Rosenstiel School of
Marine and Atmospheric Sciences, Key Biscayne, Florida,
U.S.A. - 3 Laboratory of Clinical Investigation, NIH,
Bethesda, Maryland, U.S.A. - 4 Instituto de Ciências
Biomédicas, Universidade de São Paulo, São Paulo,
Brazil. - 5 Mediacal Mycology Laboratory-HEC-FIOCRUZ,
Rio de Janeiro, Brazil. - 6 Hadassah Medical Center, Kyriat
Hadasah, Jerusalem, Israel. - 7 Molecular Mycology
Laboratory, Centre for Infectious Diseases and
Microbiology, University of Sydney, Sydney, Australia. - Email:
boekhout@cbs.knaw.nl
Cryptococcus neoformans is a basidiomycetous yeast
causing life-threatening infections in immunocompromised
hosts. The species is known in both the asexual and sexual
states. Since long two varieties C. neoformans var.
neoformans and var. gattii were known. The observation of
mating and gene flow resulted in the description of a
separate genus Filobasidiella. A third variety C.
neoformans var. grubii (= serotype A) was described
recently. Molecular studies on the IGS and ITS of the
rDNA, the mtLrRNA, URA5, laccase and phospholipase
genes, as well as AFLP and PCR-fingerprinting showed
that the three varieties belong to different phylogenetic
lineages and may represent species. Novel genotypes could
be distinguished, thus further questioning the species
boundaries. The biological species concept was tested in an
analysis of a mating between variety neoformans and
variety gattii. Most of the descendants possessed the
genotypes of either parental isolate. Gene flow could not be
demonstrated under natural circumstances. Therefore, we
proposed that both varieties represent at least two species.
Hybrid serotype AD strains of C. neoformans originated
from different parental strains. The rare serotype A MATa
allele occurs in part of these hybrids. An analysis of
virulence related phenotypic traits and antifungal
susceptibility revealed that virulence and susceptibility
varied widely. Fluconazole resistance was observed in
some environmental isolates, suggesting an innate
resistance.