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

Cesium-137 (Cs-137) 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 Cs-137 removal using algae is still limited. This is the first report to describe the kinetic properties of Cs-137 uptake by Vacuoliviride crystalliferum in the presence and absence of potassium. In this work, we studied the kinetic properties of Cs-137 uptake using a freshwater microalga, V. crystalliferum (NIES 2860). We also analyzed the effects of temperature, light, and potassium (K) on the Cs-137 uptake. Results showed that V. crystalliferum can remove up to 90% of 157 nM 137Cs within an hour. At 20 degrees C, the removal increased by up to 96%, compared to less than 10% at 5 degrees 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 from 0 to 500 mu M and the inhibitory constant (K-i) for K was determined to be 16.7 mu M. While in the uptake assay without potassium (-K), the Michaelis constant (K-m) for Cs was 45 nM and increased to 283 nM by the addition of 20 mu M potassium (+K), indicating that V. crystalliferum had a high affinity for Cs-137. In addition, the maximum uptake velocity (V-max) also increased from 6.75 to 21.10 nmol (mg Chl h)(-1), implying the existence of Cs active transport system. In conclusion, V. crystalliferum is capable of removing radioactive Cs-137 from the environment and the removal was favorable at both normal temperature and in the light.

Automated summary

This study is the first to describe the kinetic properties of Cs-137 uptake by the microalga Vacuoliviride crystalliferum and examine the effects of potassium on its absorption. Results showed that V. crystalliferum can remove up to 90% of 157 nM 137Cs within an hour, under normal temperature and light conditions.