Physiological importance and role of Mg2+ in improving bacterial resistance to cesium

Abstract

Cesium (Cs) is an alkali metal with radioactive isotopes such as 137Cs and 134Cs. 137Cs, a product of uranium fission, has garnered attention as a radioactive contaminant. Radioactive contamination remediation using microorganisms has been the focus of numerous studies. We investigated the mechanism underlying Cs+ resistance in Microbacterium sp. TS-1 and other representative microorganisms, including Bacillus subtilis. The addition of Mg2+ effectively improved the Cs+ resistance of these microorganisms. When exposed to high concentrations of Cs+, the ribosomes of Cs+-sensitive mutants of TS-1 collapsed. Growth inhibition of B. subtilis in a high-concentration Cs+ environment was because of a drastic decrease in the intracellular potassium ion concentration and not the destabilization of the ribosomal complex. This is the first study demonstrating that the toxic effect of Cs+ on bacterial cells differs based on the presence of a Cs+ efflux mechanism. These results will aid in utilizing high-concentration Cs+-resistant microorganisms for radioactive contamination remediation in the future.

Isolation and Cs+ resistance mechanism of Escherichia coli strain ZX-1

“…Our findings are particularly significant considering our prior research, which indicated that ribosomes are destabilized in the presence of Cs + but can be stabilized by magnesium ions (Ishida et al, 2023b). In addition, K + has been reported to play a role in ribosome stabilization (Nierhaus, 2014;Rozov et al, 2019).…”

“…Furthermore, higher intracellular Cs + concentrations lead to the expulsion of intracellular K + through the K + excretion system to maintain vital homeostatic processes, such as intracellular turgor pressure, resulting in a drastic decrease in intracellular K + concentration, resulting in growth inhibition (see Figure 1 ; Bossemeyer et al, 1989 ). Our group recently demonstrated that even in Bacillus subtilis , a gram-positive bacterium, the intracellular K + concentration dramatically decreases when exposed to high Cs + concentrations ( Ishida et al, 2023b ).…”