Genetic diversity of yeasts from East Ongul Island, East Antarctica and their extracellular enzymes secretion

Abstract

Microbes growing at low temperatures encounter numerous growth constraints. However, fungi that inhabit polar regions can grow and decompose organic compounds at low temperatures. Research on the biodiversity and secretion ability of yeasts from East Ongul Island, and evaluation of their extracellular enzymatic activity at temperatures ranging from −3 to 20 °C, was performed and described in this study. In total, 95 yeast strains were isolated from the surface soil on East Ongul Island, East Antarctica. Based on the internal transcribed spacer (ITS) region and 26S rDNA D1/D2 domain sequence similarity, these strains were classified into 10 genera and 16 species. All strains were categorized as basidiomycetous yeasts. One representative strain was selected from each species, and its ability to grow at temperatures between −3 and 37 °C was evaluated. Strain abilities to secrete extracellular enzymes (lipase, cellulase, and protease) at temperatures ranging from −3 to 20 °C were also investigated. Based on the optimal and maximal growth temperatures, the yeasts were classified as psychrophilic or psychrotolerant. All the strains investigated in this study were able to grow at −3 °C and in vitamin-free media. Psychrophilic yeasts, such as Glaciozyma antarctica, Gl. martinii, Mrakia gelida, and Phenoliferia glacialis, did not secrete pronounced amounts of extracellular enzymes at −3 °C; in contrast, the psychrotolerant yeasts Goffeauzyma gilvescens, Holtermanniella wattica, Tausonia pullulans, and Udeniomyces puniceus secreted copious amounts of enzymes, even at subzero temperatures. These results indicated that psychrotolerant yeasts, rather than psychrophilic yeasts, play important roles in the nutrient cycle in the East Ongul Island ecosystem at near-subzero temperatures.