46 research outputs found
The neurotropic black yeast Exophiala dermatitidis has a possible origin in the tropical rain forest
The neurotropic black yeast Exophiala dermatitidis has a possible origin in the tropical rain forest
The black yeast Exophiala dermatitidis is known as a rare
etiologic agent of neurotropic infections in humans, occurring particularly in
East and Southeast Asia. In search of its natural habitat, a large sampling
was undertaken in temperate as well as in tropical climates. Sampling sites
were selected on the basis of the origins of previously isolated strains, and
on the basis of physiological properties of the species, which also determined
a selective isolation protocol. The species was absent from outdoor
environments in the temperate climate, but present at low abundance in
comparable habitats in the tropics. Positive outdoor sites particularly
included faeces of frugivorous birds and bats, in urban as well as in natural
areas. Tropical fruits were found E. dermatitidis positive at low
incidence. Of the human-made environments sampled, railway ties contaminated
by human faeces and oily debris in the tropics were massively positive, while
the known abundance of the fungus in steam baths was confirmed. On the basis
of the species' oligotrophy, thermotolerance, acidotolerance, moderate
osmotolerance, melanization and capsular yeast cells a natural life cycle in
association with frugivorous animals in foci in the tropical rain forest,
involving passage of living cells through the intestinal tract was
hypothesized. The human-dominated environment may have become contaminated by
ingestion of wild berries carrying fungal propagule
Redefinition of Aureobasidium pullulans and its varieties
Using media with low water activity, a large numbers of aureobasidium-like
black yeasts were isolated from glacial and subglacial ice of three
polythermal glaciers from the coastal Arctic environment of Kongsfjorden
(Svalbard, Spitsbergen), as well as from adjacent sea water, sea ice and
glacial meltwaters. To characterise the genetic variability of
Aureobasidium pullulans strains originating from the Arctic and
strains originating pan-globally, a multilocus molecular analysis was
performed, through rDNA (internal transcribed spacers, partial 28 S rDNA), and
partial introns and exons of genes encoding β-tubulin (TUB),
translation elongation factor (EF1α) and elongase
(ELO). Two globally ubiquitous varieties were distinguished: var.
pullulans, occurring particularly in slightly osmotic substrates and
in the phyllosphere; and var. melanogenum, mainly isolated from
watery habitats. Both varieties were commonly isolated from the sampled Arctic
habitats. However, some aureobasidium-like strains from subglacial ice from
three different glaciers in Kongsfjorden (Svalbard, Spitsbergen), appeared to
represent a new variety of A. pullulans. A strain from dolomitic
marble in Namibia was found to belong to yet another variety. No molecular
support has as yet been found for the previously described var.
aubasidani. A partial elongase-encoding gene was successfully used as
a phylogenetic marker at the (infra-)specific level