Impact of Sinorhizobium meliloti Exopolysaccharide on Adsorption and Aggregation in the Copper(II) Ions/Supporting Electrolyte/Kaolinite System

Katarzyna Szewczuk-Karpisz,Iwona Komaniecka,Weronika Sofińska-Chmiel,Adam Choma,Agnieszka Adamczuk,Agnieszka Tomczyk

doi:10.3390/ma14081950

Katarzyna Szewczuk-Karpisz, Iwona Komaniecka + Show 4 more

Open Access

https://doi.org/10.3390/ma14081950

Copy DOI

Abstract

To obtain insight into physicochemical interactions between Cu(II) ions, kaolinite, and exopolysaccharide (EPS) synthesized by Sinorhizobium meliloti Rm 1021 soil bacteria, an adsorption, electrokinetic, and aggregation study was performed in the selected systems. The obtained data showed that supporting electrolyte type affects both EPS and Cu(II) ions adsorption. For initial Cu(II) concentration 100 mg/L, 4.36 ± 0.25 mg/g (21.80 ± 1.00%) of the ions were adsorbed in 0.001 M NaCl and 3.76 ± 0.20 mg/g (18.80 ± 1.00%) in 0.001 M CaCl2. The experimental data were best fitted to the Langmuir model as well as pseudo second-order equation. The EPS adsorbed amount on kaolinite was higher in the CaCl2 electrolyte than in NaCl one. For an initial polymer concentration of 100 mg/L, the EPS adsorbed amount was 4.69 ± 0.08 mg/g (23.45 ± 0.40%) in 0.001 M NaCl and 5.26 ± 0.15 mg/g (26.32 ± 0.75%) in 0.001 M CaCl2. In the mixed system, regardless of electrolyte type, exopolysaccharide contributed to immobilization of higher amount of copper(II) ions on the clay mineral. Also, in the samples containing heavy metal ions and exopolysaccharide simultaneously, the aggregation of kaolinite particles was the strongest. The results presented in the paper may be very helpful in soil bioremediation, especially in the development of technologies reducing the mobility of heavy metals in the environment.

Highlights

The main aim of symbiosis between Sinorhizobium bacteria and Fabaceae plants is to enable the fixation of atmospheric nitrogen
The results of Cu(II) adsorption kinetics on kaolinite, presented in Figure 1a, showed that equilibrium in the examined systems was reached after 90 min in both supporting electrolyte types
The obtained data were better fitted to the pseudo second-order (PSO) equation than to the pseudo first-order (PFO) one (Figure 1a, Table 1)

Summary

Introduction

The main aim of symbiosis between Sinorhizobium bacteria and Fabaceae plants is to enable the fixation of atmospheric nitrogen. Soil bacteria penetrate into the plant through the root hairs. An infection thread is created, which introduces the microorganisms deep into the plant s tissue (primary cortex). The step is formation of the root nodule, inside which the bacteria is transformed into bacteroids—the forms enable to atmospheric nitrogen fixation. The synthesis of proteins and enzymes necessary for N2 reduction occurs [1]. One of the most important factors in establishing symbiosis between bacteria and legume plant is exopolysaccharide (EPS)—a macromolecular compound produced by microorganisms and excreted into the environment [2]

Methods

Results

Conclusion