title: Intracellular amorphous carbonates uncover a new biomineralization process in eukaryotes.
abstract: Until now, descriptions of intracellular biomineralization of amorphous inclusions involving alkaline-earth metal (AEM) carbonates other than calcium have been confined exclusively to cyanobacteria (Couradeau et al., 2012). Here, we report the first evidence of the presence of intracellular amorphous granules of AEM carbonates (calcium, strontium, and barium) in unicellular eukaryotes. These inclusions, which we have named micropearls, show concentric and oscillatory zoning on a nanometric scale. They are widespread in certain eukaryote phytoplankters of Lake Geneva (Switzerland) and represent a previously unknown type of non-skeletal biomineralization, revealing an unexpected pathway in the geochemical cycle of AEMs. We have identified Tetraselmis cf. cordiformis (Chlorophyta, Prasinophyceae) as being responsible for the formation of one micropearl type containing strontium ([Ca,Sr]CO3), which we also found in a cultured strain of Tetraselmis cordiformis. A different flagellated eukaryotic cell forms barium-rich micropearls [(Ca,Ba)CO3]. The strontium and barium concentrations of both micropearl types are extremely high compared with the undersaturated water of Lake Geneva (the Ba/Ca ratio of the micropearls is up to 800,000 times higher than in the water). This can only be explained by a high biological pre-concentration of these elements. The particular characteristics of the micropearls, along with the presence of organic sulfur-containing compounds-associated with and surrounding the micropearls-strongly suggest the existence of a yet-unreported intracellular biomineralization pathway in eukaryotic micro-organisms.
authors.affiliation: Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
authors.forename: A
authors.initials: A
authors.lastname: Martignier
authors.affiliation: Laboratoire de Géologie de Lyon, Lyon 1 University, Villeurbanne, France.
authors.forename: M
authors.initials: M
authors.lastname: Pacton
authors.affiliation: Institute F.-A. Forel, University of Geneva, Geneva, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Filella
authors.affiliation: Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
authors.forename: J-M
authors.initials: JM
authors.lastname: Jaquet
authors.affiliation: Microbiology unit, University of Geneva, Geneva, Switzerland.
authors.forename: F
authors.initials: F
authors.lastname: Barja
authors.affiliation: Institute of Geosciences, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Pollok
authors.affiliation: Institute of Geosciences, Friedrich Schiller University Jena, Jena, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Langenhorst
authors.affiliation: Service de l'Ecologie de l'Eau (SECOE), Geneva, Switzerland.
authors.forename: S
authors.initials: S
authors.lastname: Lavigne
authors.affiliation: Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, WA, Australia.
authors.forename: P
authors.initials: P
authors.lastname: Guagliardo
authors.affiliation: Centre for Microscopy, Characterisation and Analysis, The University of Western Australia, Perth, WA, Australia.
authors.forename: M R
authors.initials: MR
authors.lastname: Kilburn
authors.affiliation: CARRTEL of Thonon-les-Bains, INRA, Thonon-les-Bains, France.
authors.forename: C
authors.initials: C
authors.lastname: Thomas
authors.affiliation: Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Martini
authors.affiliation: Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Ariztegui
mesh_terms: D002254:Carbonates / Q000032:analysis*; D000460:Chlorophyta / Q000737:chemistry* / Q000378:metabolism*; D003593:Cytoplasm / Q000737:chemistry*; D060106:Lakes / Q000382:microbiology*; D053858:Metabolic Networks and Pathways; D010839:Phytoplankton / Q000382:microbiology*; D013557:Switzerland
chemical_list: D002254:Carbonates