Intracellular amorphous carbonates uncover a new biomineralization process in eukaryotes

Area of Science:

• Geochemistry
• Microbiology
• Biomineralization

Background:

• Intracellular biomineralization of alkaline-earth metal (AEM) carbonates, excluding calcium, was previously documented only in cyanobacteria.
• This study expands the understanding of biomineralization to unicellular eukaryotes.

Purpose of the Study:

• To report the first evidence of intracellular AEM carbonate granules in unicellular eukaryotes.
• To characterize these novel inclusions, termed micropearls, and identify the organisms responsible for their formation.
• To explore the implications for geochemical cycles of AEMs.

Main Methods:

• Microscopic and chemical analysis of phytoplankters from Lake Geneva.
• Identification of micropearl composition (calcium, strontium, barium carbonates).
• Culturing and analysis of Tetraselmis cf. cordiformis.

Main Results:

• Discovery of intracellular amorphous granules of AEM carbonates (micropearls) in eukaryotic phytoplankters.
• Micropearls exhibit concentric and oscillatory zoning on a nanometric scale.
• Identified Tetraselmis cf. cordiformis and another flagellate as producers of strontium- and barium-rich micropearls, respectively, with significantly high element concentrations.

Conclusions:

• Micropearls represent a previously unknown type of non-skeletal biomineralization in eukaryotes.
• The high concentration of strontium and barium suggests a significant biological pre-concentration mechanism.
• The findings indicate a novel intracellular biomineralization pathway in eukaryotic microorganisms, impacting AEM geochemical cycles.