## 3 Results
### FTIR Band Assignment and Analysis  
Cellular mechanisms associated with the removal capacities of Pb and Cr in _C. dorsiventrale_ were also investigated using FTIR analysis. The FTIR spectra of _C. dorsiventrale_ biomass were analyzed before and after exposure to Cr and Pb in order to detect, identify and characterize potential differences due to interactions of these metallic ions with functional groups of the microalgae (Figure 6).  
The obtained spectra of _C. dorsiventrale_ biomass after exposure to Cr and Pb revealed changes in functional groups (hydroxyl, carboxyl, phosphate, amino, sulfate, etc.) compared to the control. Those changes were represented by different peaks mainly characteristic of lipids, polysaccharides, and proteins. Shifts in many groups' positions were observed after treatments with Pb and especially with Cr (Table 3).  
The difference in the absorption peaks at the region 3639-3029 cm\({}^{-1}\) revealed the existence of stretching vibration of hydroxyl (-OH) and amino (-NH\({}_{2}\)) groups. Profile modifications detected in the peaks at the region 3012-2809 cm\({}^{-1}\) showed the stretching vibration of methyl and methylene functional groups (-CH\({}_{3}\), -CH\({}_{2}\)). However, this peak was absent after Cr exposure. A band at 2118 cm\({}^{-1}\) obtained after Cr treatment and related to the carbodiimide stretching group was absent in untreated control spectra as well as after Pb exposure. Moreover, the peak at the region 1460-1420 cm\({}^{-1}\), related to carbonate carboxylate or methyl groups, existed only after Cr treatment. Focusing on  
Figure 5: Fold change of mRNA expression in _C. dorsiventrale_ cells, treated with Pb and Cr single metal ion during 72 h, relative to untreated cells for _SOD_, _CAT_, _psbA_ and _HSP70_ coding genes. Columns, mean of two different RT-PCR analyses; bars, SE.  
the 1680-1600 cm\({}^{-1}\), 1545-1540 cm\({}^{-1}\) and 1425-1330 cm\({}^{-1}\) regions, all associated with proteins and assigned to Amide I (C=O), Amide II (N-H, C-N) and carboxylate (-COO), respectively. The obtained peaks presented no significant differences between untreated and treated biomass with both ions metal Cr or Pb. Peaks around 1356 and 1191 cm\({}^{-1}\) may be attributed to the phosphorous (-PO-) and sulfur (-SO-) groups of membrane phospholipids. In this region, there were no significant changes before and after Pb treatment, contrary to Cr exposure.  
Finally, bands in the region between 1072 and 980 cm\({}^{-1}\) showed a more important peak after Cr treatment which could be due to the elongation of bonds C-C and C-O abundant in polysaccharides.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Untreated Control** & **After Pb Exposure** & **After Cr Exposure** & **Wavenumber Range** & **Functional Groups a ** \\
**(cm\({}^{-1}\))** & **(cm\({}^{-1}\))** & **(cm\({}^{-1}\))** & **(cm\({}^{-1}\))** & **(cm\({}^{-1}\))** \\ \hline
3258 & 3266 & 3295 & 3639–3029 & \(v\)O-H/\(v\) N-H \\
2921 & 2922 & \(-\) & 3012–2809 & \(v_{\text{us}}\) CH\({}_{2}\) \\ \(-\) & \(-\) & 2118 & 2270–1950 & X=C=Y \\
1637 & 1637 & 1637 & 1680–1600 & \(v\)C=O \\
1542 & 1542 & 1542 & 1545–1540 & \(\delta\) N-H, \(v\)C-N \\ \(-\) & \(-\) & 1448 & 1460–1420 & CH, C=O \\
1406 & 1406 & 1406 & 1425–1330 & \(v\) COO \\
1236 & 1237 & 1222 & 1356–1191 & \(v_{\text{us}}\) P=O, S=O \\
1025 & 1022 & 1057 & 1072–980 & \(v\) C-O \\ \hline \end{tabular}
\end{table}
Table 3: Summary of wavenumbers and corresponding functional groups.  
Figure 6: FTIR spectra of _C. dorsiventrale_ biomass before and after Cr and Pb single metal ion exposure for 14 days.