Time lapse synchrotron IR chemical imaging for observing the acclimation of a single algal cell to CO2 treatment

Algae are the main primary producers in aquatic environments and therefore of fundamental importance for the global ecosystem. Mid-infrared (IR) microspectroscopy is a non-invasive tool that allows in principle studying chemical composition on a single-cell level. For a long time, however, mid-infrared (IR) imaging of living algal cells in an aqueous environment has been a challenge due to the strong IR absorption of water. In this study, we employed multi-beam synchrotron radiation to measure time-resolved IR hyperspectral images of individual Thalassiosira weissfogii cells in water in the course of acclimation to an abrupt change of CO2 availability (from 390 to 5000 ppm and vice versa) over 75 min. We used a previously developed algorithm to correct sinusoidal interference fringes from IR hyperspectral imaging data. After preprocessing and fringe correction of the hyperspectral data, principal component analysis (PCA) was performed to assess the spatial distribution of organic pools within the algal cells. Through the analysis of 200,000 spectra, we were able to identify compositional modifcations associated with CO2 treatment. PCA revealed changes in the carbohydrate pool (1200–950 cm−1), lipids (1740, 2852, 2922 cm−1), and nucleic acid (1160 and 1201 cm−1) as the major response of exposure to elevated CO2 concentrations. Our results show a local metabolism response to this external perturbation.