Selectivity in biomineralization of barium and strontium

Minna R. Krejci, Brian Wasserman, Lydia Finney, Ian McNulty, Daniel Legnini, Stefan Vogt, Derk Joester*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


The desmid green alga Closterium moniliferum belongs to a small number of organisms that form barite (BaSO 4) or celestite (SrSO 4) biominerals. The ability to sequester Sr in the presence of an excess of Ca is of considerable interest for the remediation of 90Sr from the environment and nuclear waste. While most cells dynamically regulate the concentration of the second messenger Ca 2+ in the cytosol and various organelles, transport proteins rarely discriminate strongly between Ca, Sr, and Ba. Herein, we investigate how these ions are trafficked in C. moniliferum and how precipitation of (Ba,Sr)SO 4 crystals occurs in the terminal vacuoles. Towards this goal, we simultaneously visualize intracellular dynamics of multiple elements using X-ray fluorescence microscopy (XFM) of cryo-fixed/freeze-dried samples. We correlate the resulting elemental maps with ultrastructural information gleaned from freeze-fracture cryo-SEM of frozen-hydrated cells and use micro X-ray absorption near edge structure (micro-XANES) to determine sulfur speciation. We find that the kinetics of Sr uptake and efflux depend on external Ca concentrations, and Sr, Ba, and Ca show similar intracellular localization. A highly ion-selective cross-membrane transport step is not evident. Based on elevated levels of sulfate detected in the terminal vacuoles, we propose a "sulfate trap" model, where the presence of dissolved barium leads to preferential precipitation of (Ba,Sr)SO 4 due to its low solubility relative to SrSO 4 and CaSO 4. Engineering the sulfate concentration in the vacuole may thus be the most direct way to increase the Sr sequestered per cell, an important consideration in using desmids for phytoremediation of 90Sr.

Original languageEnglish (US)
Pages (from-to)192-202
Number of pages11
JournalJournal of Structural Biology
Issue number2
StatePublished - Nov 2011


  • Biomineralization
  • Desmid green algae
  • Ion selectivity
  • Plant physiology
  • X-ray fluorescence microscopy

ASJC Scopus subject areas

  • Structural Biology


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