Mg-rich amorphous to Mg-low crystalline CaCO3 pathway in foraminifera

Zofia Dubicka; Maciej J Bojanowski; Jelle Bijma; Ulf Bickmeyer

doi:10.1016/j.heliyon.2023.e18331

Mg-rich amorphous to Mg-low crystalline CaCO₃ pathway in foraminifera

Heliyon. 2023 Jul 17;9(7):e18331. doi: 10.1016/j.heliyon.2023.e18331. eCollection 2023 Jul.

Authors

Zofia Dubicka^{1

2}, Maciej J Bojanowski³, Jelle Bijma⁴, Ulf Bickmeyer¹

Affiliations

¹ Ecological Chemistry, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, 27-570, Germany.
² University of Warsaw, Warsaw, 02-089, Poland.
³ Institute of Geological Sciences, Polish Academy of Sciences, Warsaw, Poland.
⁴ Marine Biogeosciences, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, 27-570, Germany.

Abstract

Calcium carbonate minerals produced by marine organisms play a central role in the global carbon cycle and carbonate sedimentation, which influence the climate by regulating atmospheric CO₂ levels. Foraminifera are important marine single-celled organisms that have produced calcite shells for over 300 million years. Here, we present new observations promoting our understanding for foraminiferal biocalcification by studying Amphistegina lessonii. We integrated in vivo confocal autofluorescence and dye fluorescence imaging with elemental analysis of the cell supporting the concept that the calcite shells of foraminifera are produced via deposition of intracellularly formed Mg-rich amorphous calcium carbonate (Mg-ACC) particles that transform into a stable mineral phase. This process is likely accompanied by the activity of endosymbiotic microalgae and seawater-derived endocytic vesicles that provide calcification substrates such as DIC, Ca²⁺, and Mg²⁺. The final transformation of semi-liquid amorphous nanoparticles into a crystalline shell was associated with Mg²⁺ liberation.

Keywords: Biomineralization; Endosymbiosis; Fluorescence imaging; Foraminifera; Magnesium.