Institution: | 1. CNRS/Université de Pau et des Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Pau, France;2. Martin-Luther-Universität Halle-Wittenberg, Core Facility Proteomic Mass Spectrometry, Proteinzentrum Charles Tanford, Halle (Saale), Germany;3. ID21 Beamline, European Synchrotron Radiation Facility (ESRF), Grenoble, France;4. Bordeaux Imaging Center UMS 3420 CNRS - US4 INSERM, Pôle d'imagerie électronique, Université de Bordeaux, Bordeaux, France;5. CNRS/Université de Pau et des Pays de l'Adour/E2S UPPA, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, UMR 5254, Pau, France
Bordeaux Imaging Center UMS 3420 CNRS - US4 INSERM, Pôle d'imagerie électronique, Université de Bordeaux, Bordeaux, France
UF Sciences de la Terre et Environnement, Université de Bordeaux, Pessac, France |
Abstract: | Mixotrophic microorganisms are able to use organic carbon as well as inorganic carbon sources and thus, play an essential role in the biogeochemical carbon cycle. In aquatic ecosystems, the alteration of carbon dioxide (CO2) fixation by toxic metals such as cadmium – classified as a priority pollutant – could contribute to the unbalance of the carbon cycle. In consequence, the investigation of cadmium impact on carbon assimilation in mixotrophic microorganisms is of high interest. We exposed the mixotrophic microalga Chlamydomonas reinhardtii to cadmium in a growth medium containing both CO2 and labelled 13C-1,2] acetate as carbon sources. We showed that the accumulation of cadmium in the pyrenoid, where it was predominantly bound to sulphur ligands, impaired CO2 fixation to the benefit of acetate assimilation. Transmission electron microscopy (TEM)/X-ray energy dispersive spectroscopy (X-EDS) and micro X-ray fluorescence (μXRF)/micro X-ray absorption near-edge structure (μXANES) at Cd LIII-edge indicated the localization and the speciation of cadmium in the cellular structure. In addition, nanoscale secondary ion mass spectrometry (NanoSIMS) analysis of the 13C/12C ratio in pyrenoid and starch granules revealed the origin of carbon sources. The fraction of carbon in starch originating from CO2 decreased from 73 to 39% during cadmium stress. For the first time, the complementary use of high-resolution elemental and isotopic imaging techniques allowed relating the impact of cadmium at the subcellular level with carbon assimilation in a mixotrophic microalga. |