Black yeast members of the Herpotri

Black yeast members of the Herpotrichiellaceae
present a complex ecological behavior: They are often
isolated from rather extreme environments polluted with
aromatic hydrocarbons, while they are also regularly
involved in human opportunistic infections. A selective
technique to promote the in vitro growth of herpotrichiellaceous
fungi was applied to investigate their
ecophysiology. Samples from natural ecological niches
and man-made environments that might contain black
yeasts were enriched on an inert solid support at low
humidity and under a controlled atmosphere rich in
volatile aromatic hydrocarbons. Benzene, toluene, and
xylene were provided separately as the sole carbon and
energy source via the gas phase. The assayed isolation
protocol was highly specific toward mesophilic Exophiala
species (70 strains of this genus out of 71 isolates). Those
were obtained predominantly from creosote-treated railway
ties (53 strains), but isolates were also found on
wild berries (11 strains) and in guano-rich soil samples
(six strains). Most of the isolates were obtained on
toluene (43 strains), but enrichments on xylene and
benzene also yielded herpotrichiellaceous fungi (17 and
10 isolates, respectively). Based upon morphological
characterizations and DNA sequences of the full internal
transcriber spacers (ITS) and the 8.5S rRNA genes, the
majority of the obtained isolates were affiliated to the
recently described species Exophiala xenobiotica (32
strains) and Exophiala bergeri (nine strains). Members of
two other phylogenetic groups (24 and two strains,
respectively) somewhat related to E. bergeri were also
found, and a last group (three strains) corresponded to an
undescribed Exophiala species.