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. 2020 Jun 6;17(11):4059.
doi: 10.3390/ijerph17114059.

Sorption Mechanism and Optimization Study for the Bioremediation of Pb(II) and Cd(II) Contamination by Two Novel Isolated Strains Q3 and Q5 of Bacillus sp

Parviz Heidari  1 , Antonio Panico  2
Affiliations

Sorption Mechanism and Optimization Study for the Bioremediation of Pb(II) and Cd(II) Contamination by Two Novel Isolated Strains Q3 and Q5 of Bacillus sp

Parviz Heidari et al. Int J Environ Res Public Health. .

Abstract

The use of bacterial strains as agents in bioremediation processes could reduce the harmfulness of potential toxic elements (PTEs) from water and soil with low or even no impact on the natural ecosystems. In this study, two new metal resistant-bacterial strains (Q3 and Q5) of Bacillus sp. were isolated from a sulfurous spring and their potential (as pure cultures or mixed) to remove Pb(II) and Cd(II) from an aqueous matrix was evaluated and optimized using response surface methodology (RSM). The optimal conditions for Cd(II) removal from all tested strains combinations were observed at an initial pH 5, a temperature of 38 °C, and an initial Cd(II) concentration of 50 mg L-1, while the performance of bacterial strains on Pb(II) removal was strongly correlated to initial pH and temperature conditions. Moreover, the efficiency of bacterial strains in removing both PTEs, Pb(II) and Cd(II), from an aqueous matrix was considerably higher when they were used as a mixed culture rather than pure. According to field emission SEM (FESEM) and EDS analysis, the two bacterial strains showed different mechanisms in removing Cd(II): Bacillus sp. Q5 bio-accumulated Cd(II) in its periplasmic space, whereas Bacillus sp. Q3 bio-accumulated Cd(II) on its cell surface. On the other hand, Pb(II) is removed by chemical precipitation (lead sulfide) induced by both Bacillus sp. Q3 and Q5. This study discloses new aspects of Pb(II) and Cd(II) bioremediation mechanisms in Bacillus species that can be extremely useful for designing and operating novel PTEs bioremediation processes.

Keywords: PTEs removal; Pb precipitation; SEM; bacterial strains; bioaccumulation; bioremediation; central composite design.

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Conflict of interest statement

The author declares that there is no conflict of interest.

Figures

Figure 1
Figure 1
Phylogenic tree of the isolated bacterial strains Q3 and Q5 based on partial sequence of 16S region using a neighbor-joining method with 1000 bootstrap.
Figure 2
Figure 2
Growth rate profile of the two novel isolated bacterial strains (Q3 and Q5) at different ranges of temperature and initial pH and under contaminated condition of 100mg L−1 of Pb(II). Each point is the mean of three experimental replicates ± SD.
Figure 3
Figure 3
Effect of temperature and initial pH on Pb(II) and Cd(II) removal efficiency from bacterial strains Q3 and Q5 and their mixture (Q3 + Q5); (a) effect of temperature and initial pH on Pb(II) removal efficiency from Q3; (b) effect of temperature and initial pH on Cd(II) removal efficiency from Q3; (c) effect of temperature and initial pH on Pb(II) removal efficiency from Q5; (d) effect of temperature and initial pH on Cd(II) removal efficiency from Q5; (e) effect of temperature and initial pH on Pb(II) removal efficiency from the mixture of Q3 with Q5; (f) effect of temperature and initial pH on Cd(II) removal efficiency from the mixture of Q3 with Q5.
Figure 4
Figure 4
Effect of temperature and metal concentration on Pb(II) and Cd(II) removal efficiency from bacterial strains Q3 and Q5 and their mixture (Q3 + Q5): (a) effect of temperature and metal concentration on Pb(II) removal efficiency from Q3; (b) effect of temperature and metal concentration on Cd(II) removal efficiency from Q3; (c) effect of temperature and metal concentration on Pb(II) removal efficiency from Q5; (d) effect of temperature and metal concentration on Cd(II) removal efficiency from Q5; (e) effect of temperature and metal concentration on Pb(II) removal efficiency from the mixture of Q3 with Q5; (f) effect of temperature and metal concentration on Cd(II) removal efficiency from the mixture of Q3 with Q5.
Figure 5
Figure 5
Effect of initial pH and metal concentration on Pb(II) and Cd(II) removal efficiency from bacterial strains Q3 and Q5 and their mixture (Q3 + Q5): (a) effect of metal concentration and initial pH on Pb(II) removal efficiency from Q3; (b) effect of metal concentration and initial pH on Cd(II) removal efficiency from Q3; (c) effect of metal concentration and initial pH on Pb(II) removal efficiency from Q5; (d) effect of metal concentration and initial pH on Cd(II) removal efficiency from Q5; (e) effect of metal concentration and initial pH on Pb(II) removal efficiency from the mixture of Q3 with Q5; (f) effect of metal concentration and initial pH on Cd(II) removal efficiency from the mixture of Q3 with Q5.
Figure 6
Figure 6
Scanning Electron Microscopy (SEM) of cell biomass of Bacillus sp. Q3 (a) and Bacillus sp. Q5 (b) at 50 mg L−1 of Cd(II); Bacillus sp. Q3 (c) and Bacillus sp. Q5 (d) at 100 mg L−1 of Pb (d). The arrow in Figure 6a represents the bio-accumulated Cd (II) in the cell surface of Bacillus sp. Q3.
Figure 7
Figure 7
Energy Dispersive Spectrometer (EDS) analysis for elemental composition of precipitates from negative control tests (a), cell biomass of Bacillus sp. Q3 (b) and Bacillus sp. Q5 (c) at 50 mg L−1 of Cd(II).
Figure 7
Figure 7
Energy Dispersive Spectrometer (EDS) analysis for elemental composition of precipitates from negative control tests (a), cell biomass of Bacillus sp. Q3 (b) and Bacillus sp. Q5 (c) at 50 mg L−1 of Cd(II).
Figure 8
Figure 8
Energy Dispersive Spectrometer (EDS) analysis for elemental composition of precipitates from negative control tests (a), cell biomass of Bacillus sp. Q3 (b) and Bacillus sp. Q5 (c) at 100 mg L−1 of Pb.
Figure 8
Figure 8
Energy Dispersive Spectrometer (EDS) analysis for elemental composition of precipitates from negative control tests (a), cell biomass of Bacillus sp. Q3 (b) and Bacillus sp. Q5 (c) at 100 mg L−1 of Pb.
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