ABSTRACT
Cesium ion (Cs+) resistance has been reported in bacteria but is poorly understood as reports on Cs+-resistant bacteria have been limited. We previously reported a novel Cs+/H+ antiporter CshA implicated in Cs+-resistance in Microbacterium sp. TS-1. The present study used the same screening method to isolate novel Cs+-sensitive mutants and their revertants from TS-1. A comparative mutation site analysis using whole-genome sequencing revealed that MTS1_03028 encodes the Mg2+ transporter MgtE and is a candidate Cs+ resistance-related gene. We performed a bioinformatic analysis of MTS1_03028 and complementation experiments on Cs+ resistance in the TS-1 MTS1_03028 mutants Mut5 and Mut7 as well as Escherichia coli expressing MTS1_03028 in the presence of Mg2+. We established the role of MgtE in Cs+ resistance through a functional analysis of TS-1. Enhancing Mg2+ transport by expression of MTS_03028 conferred increased Cs+ resistance. When this strain was exposed to Cs+ concentrations exceeding 200 mM, CshA consistently lowered the intracellular Cs+ concentration. To our knowledge, the present study is the first to clarify the mechanism of Cs+ resistance in certain bacteria. The study findings offer important insights into the mechanism of bacterial resistance to excess Cs+ in the environment, suggesting the potential for bioremediation in high Cs-contaminated areas.
ABSTRACT
[This corrects the article DOI: 10.3389/fmicb.2022.841821.].
ABSTRACT
The radionuclide isotopes (134Cs and 137Cs) of Cesium (Cs), an alkali metal, are attracting attention as major causes of radioactive contamination. Although Cs+ is harmful to the growth of plants and bacteria, alkaliphilic bacterium Microbacterium sp. TS-1, isolated from a jumping spider, showed growth even in the presence of 1.2 M CsCl. The maximum concentration of Cs+ that microorganisms can withstand has been reported to be 700 mM till date, suggesting that the strain TS-1 is resistant to a high concentration of Cs ions. Multiple reports of cesium ion-resistant bacteria have been reported, but the detailed mechanism has not yet been elucidated. We obtained Cs ion-sensitive mutants and their revertant mutants from strain TS-1 and identified a Cs ion resistance-related gene, MTS1_00475, by performing SNP analysis of the whole-genome sequence data. When exposed to more than 200 mM Cs+ concentration, the intracellular Cs+ concentration was constantly lowered by MTS1_00475, which encodes the novel low-affinity Cs+/H+ antiporter. This study is the first to clarify the mechanism of cesium resistance in unexplained cesium-resistant microorganisms. By clarifying the new cesium resistance mechanism, it can be expected to be used as a bioremediation tool for treating radioactive Cs+ contaminated water.
