Evolution of the scattering properties of phytoplankton cells from flow cytometry measurements

• Published in: PloS one Vol. 12; no. 7; p. e0181180
• Main Authors: Moutier, William, Duforêt-Gaurier, Lucile, Thyssen, Mélilotus, Loisel, Hubert, Mériaux, Xavier, Courcot, Lucie, Dessailly, David, Rêve, Anne-Hélène, Grégori, Gérald, Alvain, Séverine, Barani, Aude, Brutier, Laurent, Dugenne, Mathilde
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 14.07.2017; Public Library of Science (PLoS)
• Subjects: Algorithms; Atoms & subatomic particles; Biogeochemistry; Biology and Life Sciences; Chlorophyta - cytology; Chlorophyta - growth & development; Chloroplasts; Chloroplasts - chemistry; Chloroplasts - metabolism; Computer simulation; Cytometry; Cytoplasm; Diatoms - cytology; Diatoms - growth & development; Ecology, environment; Evolution; Evolution (Biology); Flow Cytometry; Growth stage; Life cycle engineering; Life Cycle Stages; Life cycles; Life Sciences; Light; Limnology; Microscopy, Electron, Scanning; Morphology; Oceanography; Optical measurement; Optical properties; Optics; Physical Sciences; Phytoplankton; Plankton; Population growth; Principal Component Analysis; Radiative transfer; Refractive index; Refractivity; Research and Analysis Methods; Scattering; Scattering (Physics); Simulation; Variability
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0181180

After the exponential growth phase, variability in the scattering efficiency of phytoplankton cells over their complete life cycle is not well characterised. Bulk measurements are impacted by senescent cells and detritrus. Thus the analysis of the evolution of the optical properties thanks to their morphological and/or intra-cellular variations remains poorly studied. Using the Cytosense flow cytometer (CytoBuoy b.v., NL), the temporal course of the forward and sideward efficiencies of two phytoplankton species (Thalassiosira pseudonana and Chlamydomonas concordia) were analyzed during a complete life-cycle. These two species differ considerably from a morphological point of view. Over the whole experiment, the forward and sideward efficiencies of Thalassiosira pseudonana were, on average, respectively 2.2 and 1.6 times higher than the efficiencies of Chlamydomonas concordia. Large intra-species variability of the efficiencies were observed over the life cycle of the considered species. It highlights the importance of considering the optical properties of phytoplankton cells as a function of the population growth stage of the considered species. Furthermore, flow cytometry measurements were combined with radiative transfer simulations and biogeochemical and optical measurements. Results showed that the real refractive index of the chloroplast is a key parameter driving the sideward signal and that a simplistic two-layered model (cytoplasm-chloroplast) seems particularly appropriate to represent the phytoplankton cells.