Yeasts and Yeast-Like Fungi as an Element of Purity Assessment of Surface Waters

The aim of our study was to determine species biodiversity of yeasts and yeast-like fungi in the stratum of surface water of Lake Tyrsko, as well as to evaluate the condition of waters of that lake based on the isolated species of fungi. The study was carried out from June 2007 to June 2008. The isolation and determination of the number of fungal colonies were conducted with the use of the membrane filter method. Fungal diagnostics were conducted based on the morphological and biochemical characteristics of the fungi. These characteristics were additionally used for taxonomic identification. In the course of the study we isolated 56 species of yeasts and yeast-like fungi belonging to 26 genera, with the predominating genus being Kluyveromyces (13 species), followed by less frequent genera: Candida (8 species), and Debaryomyces (7 species). The highest number of isolates were obtained in the spring (51), fewer in the summer (36), and the lowest in autumn (15). Species indicatory of the self-purifying process of the water examined were frequently isolated (Debaryomyces hansenii, Pichia membranifaciens). Results obtained in the study confirm suggestions of other authors that yeasts and yeast-like fungi may be useful as indicatory organisms showing the extent and character of water contamination and as bioindicators of sanitary and hygienic evaluation of water.