Bonding Behavior and Mechanism of U(VI) by Chemically Modified Deinococcus radiodurans

Xiaoqin Nie,Liang Bian,Wencai Cheng,Faqin Dong,Shiyong Sun,Mingxue Liu,Congcong Ding

doi:10.3390/min11101108

Abstract

The goal of this study is to understand the role of various functional groups on the cell surface when the microorganisms are exposed to uranium (U(VI)). The biomass of Deinococcus radiodurans was subjected to chemical treatments to modify the carboxyl (-C=O), amino (-NH2), phosphate (-PO2−), and hydroxyl (-OH) groups, as well as the lipid fraction. The behavior and process of U(VI) biosorption by Deinococcus radiodurans were ascertained, followed by scanning electron microscopy (SEM) combined with energy disperse spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) analyses. Carboxyl esterification and amino methylation deteriorated the removal efficiency by 8.0% and 15.5%, respectively, while lipid extraction, phosphate esterification, and hydroxyl methylation improved the removal efficiency by 11.7%, 8.7%, and 4.1%, respectively. The kinetic results revealed that uranium biosorption behavior by the raw and chemically modified biomass fitted well with the model of pseudo-second-order kinetic (R2 = 0.9949~0.9998). FTIR and SEM-EDS indicated that uranium initially bound with the raw and chemically modified Deinococcus radiodurans, which was probably controlled by ion exchange at the first stage, followed by complexation with the -C=O and -NH2 groups, which especially prefer to bond with P and O atoms on the -PO2− group.

Highlights

With the fast development of the nuclear industry, the treatment and remediation of the nuclear, especially uranium (U(VI)), waste environment are still a common concern [1,2,3,4,5]
We focus on the role of functional groups on typical radiation-resistant bacterium, and the aims of this study are as follows: (1) to investigate the role and behavior of the main functional groups on the cell surface of Deinococcus radiodurans by chemical modification and batch experiment; and (2) to identify the mechanism of bonding between Deinococcus radiodurans and uranium via a combination of scanning electron microscopy (SEM)-energy disperse spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), NMR, HPLC, and X-ray diffraction (XRD)
Carboxyl esterification and amino methylation led to uranium removal efficiency decrease of 8.0% and 15.5%, respectively

Summary

Introduction

With the fast development of the nuclear industry, the treatment and remediation of the nuclear, especially uranium (U(VI)), waste environment are still a common concern [1,2,3,4,5]. Several investigators have reported the potential of living and dead biomass of microbial origin to remove uranium from solutions [6,7,8,9,10,11]. Bioremediation of uranium waste by microbes offers a good alternative to physiochemical methods in terms of in situ applicability and high removal efficiency at a rather low concentration of the metal ion [12]. The main processes that are currently employed in uranium bioremediation include enzymatic metal bioreduction of soluble U(VI) to sparingly soluble U(IV), adsorption on cell surface, biopolymers or dead biomass, and bioprecipitation of U(VI) with ligands like inorganic phosphate [7,11].

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Conclusion