Abstract
The environmental isolation of opportunistic pathogenic black yeasts, which are responsible for a wide spectrum of human infections, is essential to understanding the ecology of clinical fungi. Extreme outdoor environments polluted with aromatic hydrocarbons support the growth of black yeasts in unlikely places, such as railway sleepers. However, there are limited data concerning the diversity of these fungi growing on polluted railway sleepers. In this investigation, we examined 845 railway sleeper samples, obtained from 11 Turkish cities representing altitudes from 25 to 1,893 m, and inoculated the samples onto mycological media for the isolation of black yeasts. Ninety-four samples (11.1 %) yielded positive results for black yeast, with creosoted oak sleepers having a significantly higher number of isolates than concrete sleepers (p < 0.05). Identification based on the ribosomal DNA (rDNA) internal transcribed spacer region revealed the highest prevalence of Exophiala phaeomuriformis, followed by Exophiala dermatitidis, Exophiala heteromorpha, Exophiala xenobiotica, and Exophiala crusticola. This study revealed that railway sleepers harboring black yeasts were predominantly (>75 %) populated with thermophilic species. We observed that altitude might have a significant effect on species diversity. Briefly, E. phaeomuriformis exhibited growth over a wide altitude range, from 30 to 1,893 m. In contrast, E. dermatitidis had a remarkable aversion to low altitudes and exhibited maximum growth at 1,285 m. In conclusion, we speculate that one can predict what species will be found on railway sleepers and their probability and that species diversity primarily depends on sleeper type and altitude height. We believe that this study can contribute new insights into the ecology of black yeasts on railway sleepers and the railway factors that influence their diversity.
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Acknowledgments
The authors would like to thank Professor Süleyha Hilmioglu-Polat for the assistance with the collection of the Izmir samples, Associate Professor Aylin Dogen for conducting the physiological analysis, and Professor Refik Burgut for the statistical analysis of the study data. The authors would also like to thank the staff of the CBS-KNAW Fungal Biodiversity Centre collection service, specifically Mrs. Trix Merkx and Mr. Gerard Verkleij, for processing several of the Exophiala isolates.
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The authors report no conflicts of interest. The authors alone are responsible for the content and composition of this manuscript.
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Gümral, R., Tümgör, A., Saraçlı, M.A. et al. Black Yeast Diversity on Creosoted Railway Sleepers Changes with Ambient Climatic Conditions. Microb Ecol 68, 699–707 (2014). https://doi.org/10.1007/s00248-014-0459-5
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DOI: https://doi.org/10.1007/s00248-014-0459-5