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. 2020 Mar 30;8(4):491.
doi: 10.3390/microorganisms8040491.

Behavior and Mechanism of Cesium Biosorption from Aqueous Solution by Living Synechococcus PCC7002

Runlan Yu  1 , Hongsheng Chai  1 , Zhaojing Yu  1 , Xueling Wu  1 , Yuandong Liu  1 , Li Shen  1 , Jiaokun Li  1 , Jun Ye  2 , Danchan Liu  2 , Tao Ma  2 , Fengzheng Gao  3 , Weimin Zeng  1
Affiliations

Behavior and Mechanism of Cesium Biosorption from Aqueous Solution by Living Synechococcus PCC7002

Runlan Yu et al. Microorganisms. .

Abstract

Many efforts have focused on the adsorption of metals from contaminated water by microbes. Synechococcus PCC7002, a major marine cyanobacteria, is widely applied to remove metals from the ocean's photic zone. However, its ability to adsorb cesium (Cs) nuclides has received little attention. In this study, the biosorption behavior of Cs(I) from ultrapure distilled water by living Synechococcus PCC7002 was investigated based on kinetic and isotherm studies, and the biosorption mechanism was characterized by Fourier-transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometry, and three-dimensional excitation emission matrix fluorescence spectroscopy. Synechococcus PCC7002 showed extremely high tolerance to Cs ions and its minimal inhibitory concentration was 8.6 g/L. Extracellular polymeric substances (EPS) in Synechococcus PCC7002 played a vital role in this tolerance. The biosorption of Cs by Synechococcus PCC7002 conformed to a Freundlich-type isotherm model and pseudo-second-order kinetics. The binding of Cs(I) was primarily attributed to the extracellular proteins in EPS, with the amino, hydroxyl, and phosphate groups on the cell walls contributing to Cs adsorption. The biosorption of Cs involved two mechanisms: Passive adsorption on the cell surface at low Cs concentrations and active intracellular adsorption at high Cs concentrations. The results demonstrate that the behavior and mechanism of Cs adsorption by Synechococcus PCC7002 differ based on the Cs ions concentration.

Keywords: Biosorption; Cs; EPS; Synechococcus PCC7002.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Growth curves of Synechococcus PCC7002 under different concentrations of Cs(I).
Figure 2
Figure 2
EPS production by Synechococcus PCC7002 under different concentrations of Cs(I).
Figure 3
Figure 3
Kinetics of Cs(I) adsorption on Synechococcus PCC7002 in aqueous solution fitted using the pseudo-first-order model (a) and pseudo-second-order model (b).
Figure 4
Figure 4
Langmuir isotherms (a) and Freundlich isotherms (b) of Cs(I) adsorption on Synechococcus PCC7002.
Figure 5
Figure 5
FTIR spectra of Synechococcus PCC7002 (a) and Cs-loaded Synechococcus PCC7002 (b).
Figure 6
Figure 6
SEM images of Synechococcus PCC7002 (a) and Cs-loaded Synechococcus PCC7002 (b). Scale bars: (a) 1 μm; (b) 1 μm.
Figure 7
Figure 7
EDX spectra of Synechococcus PCC7002 (a) and Cs-loaded Synechococcus PCC7002 (b). The elements analyzed were C, O, Cl, P, Na, K, and Cs.
Figure 8
Figure 8
Excitation emission matrix (EEM) fluorescence spectra of extracellular polymeric substances (EPS) from Synechococcus PCC7002 (a) and Cs-loaded Synechococcus PCC7002 (b).
Figure 9
Figure 9
TEM images and corresponding EDX spectra of Synechococcus PCC7002 before and after the adsorption of Cs at different concentrations: (a,d) 0 g/L (untreated biomass), (b,e) 0.5 g/L, and (c,f) 5 g/L of Cs ions. The red circles in the TEM images indicate the locations of EDX analysis. The arrows in Figure 9c indicate the precipitates in the cytoplasm, which demonstrate the intracellular uptake of Cs ions.
See this image and copyright information in PMC

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