Conceptualization, T.B. and I.M.; methodology, I.M.; formal analysis, T.B. and K.H.; resources, I.M.; data curation, T.B. and K.H.; writing—original draft preparation, T.B. and I.M.; writing—review and editing, I.M.; funding acquisition, I.M. All authors have read and agreed to the published version of the manuscript.

Figure 1. Images of SEM and the elemental mapping of C, O, and Pb in P. margaritaceum cells. Pb-treated NIES-217 (A) and NIES-303 (B) cells were observed.

Figure 1. Images of SEM and the elemental mapping of C, O, and Pb in P. margaritaceum cells. Pb-treated NIES-217 (A) and NIES-303 (B) cells were observed.

Figure 2. Observations of P. margaritaceum NIES-303 culture, the immobilized cells, and soaking of the immobilized cells in the Pb solution. The algal culture (A) was filtrated using filter paper to prepare the immobilized cells (B), which was soaked in the Pb solution with gentle shaking for 8 h (C).

Figure 2. Observations of P. margaritaceum NIES-303 culture, the immobilized cells, and soaking of the immobilized cells in the Pb solution. The algal culture (A) was filtrated using filter paper to prepare the immobilized cells (B), which was soaked in the Pb solution with gentle shaking for 8 h (C).

Figure 3. Time course of Pb concentration as the immobilized cells were soaked in the aqueous solution. Plots with an error bar show means (n = 3) ± SD.

Figure 3. Time course of Pb concentration as the immobilized cells were soaked in the aqueous solution. Plots with an error bar show means (n = 3) ± SD.

Figure 4. Specificity of Pb removal in the presence of divalent and monovalent cations during the soaking immobilized cells in the aqueous solution. Blue (Na), green (K), gray (Ca), yellow (Mg), and red (Pb) bars with an error bar show the means (n = 3) ± SD at 0 h and after soaking for 8 h. ND indicates that Pb was not detected.

Figure 4. Specificity of Pb removal in the presence of divalent and monovalent cations during the soaking immobilized cells in the aqueous solution. Blue (Na), green (K), gray (Ca), yellow (Mg), and red (Pb) bars with an error bar show the means (n = 3) ± SD at 0 h and after soaking for 8 h. ND indicates that Pb was not detected.

Figure 5. FT-IR spectra of the algal cells treated with and without the Pb solution. Cells of NIES-217 (A) and NIES-303 (B) were compressed in KBr plates before (upper spectra) and after (lower spectra) suspension of cells in the Pb solution.

Figure 5. FT-IR spectra of the algal cells treated with and without the Pb solution. Cells of NIES-217 (A) and NIES-303 (B) were compressed in KBr plates before (upper spectra) and after (lower spectra) suspension of cells in the Pb solution.

Table 1. Dry weights of the immobilized algal cells and insoluble materials at the bottom of the flask after soaking, and the optical densities at 0 h and after soaking.

Table 1. Dry weights of the immobilized algal cells and insoluble materials at the bottom of the flask after soaking, and the optical densities at 0 h and after soaking.

ImmobilizationFilter Paper (mg) *Flask Bottom (mg) *OD600 at 0 hOD600 at 8 hNIES-2179.5 ± 1.11.6 ± 0.70.018 ± 0.0020.016 ± 0.001NIES-30317.5 ± 3.00.4 ± 0.40.016 ± 0.0010.016 ± 0.002

Table 2. Removal and recovery of Pb by the immobilized cells at 0 h and after soaking for 8 h.

Table 2. Removal and recovery of Pb by the immobilized cells at 0 h and after soaking for 8 h.

ImmobilizationTimeSolution (µg) *Filter Paper (µg) *Flask Bottom (µg) *Recovery (µg) *Recovery %NIES-2170 h90.9 ± 1.4––––8 h41.0 ± 11.632.7 ± 1.822.7 ± 6.496.3 ± 16.096.3NIES-3030 h92.0 ± 2.1––––8 h46.7 ± 10.031.8 ± 6.420.4 ± 15.698.9 ± 6.198.9No alga0 h96.9 ± 5.8––––8 h96.2 ± 1.20.2 ± 0.4ND96.4 ± 2.796.4