Kinetic properties of 137Cs uptake by the cesium-accumulating eustigmatophycean microalga.

Abstract

Cesium-137 (137Cs) is one of the radioactive substances that was released into the environment as a result of the Fukushima nuclear disaster. Radiocesium exposure is of great concern due to its potential environmental implications. However, research on 137Cs removal using algae is still limited. This is the first report todescribe the kinetic properties of 137Cs uptake by Vacuoliviride crystalliferum in the presenceand absence of potassium. In this work, we studied the kinetic properties of 137Cs uptake using a freshwater microalga, V. crystalliferum (NIES 2860). We also analyzed the effects of temperature, light, and potassium (K) on the 137Cs uptake. Results showed that V. crystalliferum can remove up to 90% of 157nM 137Cs within an hour. At 20°C, the removal increased by up to 96%, compared to less than 10% at 5°C. However, the removal was inhibited by nearly 90% in the dark compared to the removal in the light, implying that V. crystalliferum cells require energy to accumulate 137Cs. In the inhibition assay, K concentrations ranged from0 to 500µM and the inhibitory constant (Ki) for K was determined to be 16.7µM. While in the uptake assay without potassium (- K), the Michaelis constant (Km) for Cs was 45nM and increased to 283nM by the addition of 20µM potassium (+ K), indicating that V. crystalliferum had a high affinity for 137Cs. In addition, the maximum uptake velocity (Vmax) also increased from 6.75 to 21.10nmol (mg Chl h)-1, implying the existence of Cs active transport system. In conclusion, V. crystalliferum is capable of removing radioactive 137Cs from the environment and the removal was favorable at both normal temperature and in the light.