Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Remediation of heavy-metal-contaminated sites represents a serious environmental problem worldwide. Currently, cost- and time-intensive chemical treatments are mainly performed. Bioremediation by heavy-metal-tolerant microorganisms is considered a more eco-friendly and comparatively cheap alternative. The fungus KS1 (Penicillium simplicissimum), isolated from the flooding water of a former uranium (U) mine in Germany, shows promising U bioremediation potential mainly through biomineralization. The adaption of KS1 to heavy-metal-contaminated sites is indicated by an increased U removal capacity of up to 550 mg U per g dry biomass compared to the non-heavy-metal-exposed P. simplicissimum reference strain DSM 62867 (200 mg U per g dry biomass). In addition, the effect of temperature and cell viability of KS1 on U biomineralization was investigated. While viable KS1 cells at 30 °C removed U mainly extracellularly via metabolism-dependent biomineralization, a decrease in temperature to 4 °C or implementation of dead-autoclaved KS1 cells at 30 °C revealed increased occurrence of passive biosorption and bioaccumulation, as observed by scanning transmission electron microscopy. The precipitated U species were assigned to uranyl phosphates with a structure similar to that of autunite via cryo-time-resolved laser fluorescence spectroscopy. The major involvement of phosphorus in U precipitation by the fungus KS1 was additionally supported by the observation of increased phosphatase activity for viable cells at 30 °C. Furthermore, viable KS1 cells actively secreted small molecules, most likely phosphorylated amino acids, which interacted with U in the supernatant and were not detected in experiments with dead-autoclaved cells. Our studies provide new insights into the influence of temperature and cell viability on U phosphate biomineralization by fungi and highlight the potential use of KS1 particularly for U bioremediation purposes.