Simultaneous removal of caesium and strontium using different removal mechanisms of probiotic bacteria

Abstract

When radioactive materials are released into the environment due to nuclear power plant accidents, they may enter into the body, and exposing it to internal radiation for long periods of time. Although several agents have been developed that help excrete radioactive elements from the digestive tract, only one type of radioactive element can be removed using a single agent. Therefore, we considered the simultaneous removal of caesium (Cs) and strontium (Sr) by utilising the multiple metal removal mechanisms of probiotic bacteria. In this study, the Cs and Sr removal capacities of lactobacilli and bifidobacteria were investigated. Observation using an electron probe micro analyser suggested that Cs was accumulated within the bacterial cells. Since Sr was removed non metabolically, it is likely that it was removed by a mechanism different from that of Cs. The amount of Cs and Sr that the cells could simultaneously retain decreased when compared to that for each element alone, but some strains showed only a slight reduction in removal. For example, Bifidobacterium adolescentis JCM1275 could simultaneously retain 55.7 mg-Cs/g-dry cell and 8.1 mg-Sr/g-dry cell. These results demonstrated the potentials of utilizing complex biological system in simultaneous removal of multiple metal species.

Figure 1

Caesium (Cs), phosphorus (P), and potassium (K) distribution and backscattered electron images (COMPO) of bacterial cells. Element maps show that the concentration of each element is higher at the point where the measurement level is higher.

Figure 2

Growth curves of lactobacilli and bifidobacteria on Cs-supplemented medium. The vertical axis shows unit optical density at 680 nm (U.O.D.₆₈₀). Each legend indicates the concentration of caesium supplemented to the medium. Error bars represent the standard error (n = 3).

Figure 3

Experimental design for removal of Cs and Sr by bacteria.

Figure 4

Amount of Cs and Sr contained in each bacterium. Cs ( +) indicates the addition of 50 mM Cs to the culture medium, and Sr (+ ) indicates the suspension of cells in the solution containing 1 mM Sr. Error bars represent the standard error (n = 3).