Characterization of Radiation-Resistant Yeast Isolated from Radiation-Polluted Areas and Its Potential Application in Bioremediation

Abstract

Twenty-four yeast isolates were obtained from radiation-polluted areas soils samples exposed to 60Co-γ radiation at a dose of 10 kGy and identified as members of the genus Cryptococcus based on morphological and LSU rDNA D1/D2 domain sequence analysis. Further phylogenetic analysis showed that the isolates were clustered into 4 branches. The investigation of these yeast isolates revealed D10 values for γ radiation of 5 (M2), 5 (M38), 6 (M22) and 7 kGy (M5) and a 4 × 10–3% survival rate at a UV dosage of 200 J/m2. Furthermore, the tolerance of M5 towards Zn2+ was as high as 1.700 mg/L. The isolate M5 was selected for further study, including the distribution of heavy metals within the cells by subcellular fractionation, expression of relevant genes involved in heavy metal resistance by qRT-PCR, and the removal rate by flame atomic absorption spectrometry (FAAS). The results revealed that almost 72.9% of the Zn2+ was absorbed by the cells and deposited mainly in the membrane fraction. Compared to normal conditions, all of the genes in M5 strain related to transport and regulation showed greater than 10.4-fold increases of expression levels upon exposure to heavy metal stress. In the presence of culture medium, a total of 86.5% of the initial concentration of Zn2+ was removed by the M5 strain exhibiting high removal efficiency and providing a potential of radiation-resistant platform strain for the bioremediation of heavy metals in polluted environments in the near future.