Vacuoles Sequester Strontium

Biological Strategy

Desmid green algae

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Chemically Assemble Mineral Crystals

The vast majority of biochemical assembly and break down processes––even by the most complex organisms––occur within cells. In fact, cells are able to perform hundreds, even thousands, of chemical transformations at the same time under life-friendly conditions (ambient temperature and pressure in an aqueous environment). Within cells, organisms utilize organic compounds to facilitate the assembly of mineral crystals. For example, oysters utilize acidic proteins and sulfated polysaccharides to assemble layers of aragonite crystals.

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Modify Concentration (of Ions, Solutes, Etc.)

Modifying the concentration of chemical constituents in solution or in materials allows for controlling the outcome of chemical processes or the functional characteristics of materials. For example, sulfur groups have an affinity for dissolved calcium ions. When oysters secrete a self-assembling organic matrix decorated with immobilized sulfur groups, they attract and concentrate calcium ions in the surrounding seawater. In turn, the high concentration of positively charged calcium ions attract negatively charged carbonate ions which triggers the stepwise formation of amorphous, and then crystalline, calcium carbonate.

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Protists

Kingdom Protista (“the very first”): slime molds, giant kelp, red and brown algae

Protists are a numerous, diverse group of organisms that, in the simplest definition, are defined by what they are not. Protists are not plants, animals, fungi, or bacteria. Some protists, like Plasmodium, are harmful parasites that cause malaria. While many are small, obscure, and go unnoticed, others are important foodstuffs. The largest protist in the world, giant kelp (Macrocystis pyrifera), is utilized by humans and marine species for food and shelter.

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Vacuoles in desmid green algae sequester Sr in the presence of excess calcium through a sulfate trap where the presence of dissolved barium leads to preferential precipitation of (Ba,Sr)SO4.

Many are known for their ability to sequester carbon dioxide through the precipitation of calcium carbonate but not many have been known to precipitate biominerals containing barium or strontium. What sets desmid green algae apart is its ability to sequester strontium (Sr) and barium (Ba). Sr and Ba are chemically very similar to calcium and when the elemental molecules are in the presence of one another, calcium often “outcompetes” the other two in forming a precipitant. However, researchers have found that when there is a large amount of dissolved barium in vacuoles where calcium and strontium are concentrated, the bacteria precipitates (Ba, Sr)SO4. They atrribute this finding to (Ba,Sr)SO4’s low solubility compared to other options for biomineral precipitants. 90Sr is a harmful radioactive element that has been linked to cancer as it can substitute for calcium in bone. In addition, during environmental disasters, cleanup teams struggle with removing 90Sr in the presence of calcium because of competition between the two for uptake.

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Last Updated August 23, 2016

References

Journal article

Selectivity in biomineralization of barium and strontium

Journal of Structural Biology | 26/08/2011 | Minna R. Krejci, Brian Wasserman, Lydia Finney, Ian McNulty, Daniel Legnini, Stefan Vogt, Derk Joester

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