Novel Cesium Resistance Mechanism of Alkaliphilic Bacterium Isolated From Jumping Spider Ground Extract.

Masahiro Ito,Eri Ishiuchi,Yoshiki Ishida,Takahiro Koretsune,Nanami Marubashi,Katsuya Satoh,Miyu Teshima,Yuri Kaneda

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.

Highlights

Cesium (Cs) is an alkali metal, and 134Cs and 137Cs are radioactive isotopes
Escherichia coli and B. subtilis grew in a medium containing up to 50 mM CsCl, but the TS-1 strain grew up to1200 mM CsCl
Escherichia coli increased the intracellular Cs+ concentration in correlation with CsCl added to the medium, strain TS-1 kept the intracellular Cs+ concentration low even when exposed to CsCl of 200 mM or more

Summary

Introduction

Cesium (Cs) is an alkali metal, and 134Cs and 137Cs are radioactive isotopes. Radioactive 137Cs is produced from nuclear power generation waste and has attracted considerable attention as a major causative agent of radioactive contamination (Buesseler et al, 2012). Studies have reported that Cs+ uptake into cells via the K+ uptake system is localized in the cell membrane of plants and bacteria and high concentrations of Cs+ are toxic (Perkins and Gadd, 1995; Hampton et al, 2004), because of decreased intracellular K+ concentration due to the influx of Cs+ into. Cesium Resistance Mechanism of Alkaliphilic Bacterium the cell (Bossemeyer et al, 1989; Jung et al, 2001). In Escherichia coli, as it lacks a Cs+ efflux system, Cs+ influx into cells occurs through the Kup system, the main K+ uptake system (Bossemeyer et al, 1989), resulting in an increased intracellular Cs+ concentration. The decrease in intracellular K+ concentration inhibited the growth of E. coli (Bossemeyer et al, 1989). The expression of the kdpFABC operon, which encodes a highaffinity K+ uptake system, is induced to compensate for the decrease in intracellular K+ concentration (Jung et al, 2001)

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