Characterisation of Pb-induced changes and prediction of Pb exposure in microalgae using infrared spectroscopy

Macromolecular changes in Chlorella sp. FleB1 and Scenedesmus acutus YaA6 exposed to Pb were characterised by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. Spectra were collected in the mid-infrared spectral region and a chemometric approach was used to analyse the spectra. Principal Component Analysis showed that under Pb treatment, carbohydrates and lipids increased while proteins and phosphorylated molecules decreased in both the isolates. These conclusions were corroborated by conventional measurements of photosynthesis and neutral lipids. In the two strains, Pb inhibited photosynthesis, which directly affects the synthesis of polysaccharides and other macromolecules. Neutral lipids as measured by Nile Red were increased in lead-treated samples. Modelling of spectral data against Pb exposure levels allowed Pb-exposed samples to be readily discriminated from unexposed controls and the level of Pb exposure could be predicted with good accuracy in independent validation testing. This study demonstrates the utility of the spectroscopic approach as a rapid, inexpensive, non-destructive method to understand changes in cellular composition induced by Pb and allowing detection and quantification of Pb levels in metal-contaminated cells in a "snapshot".