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This study arose from an accidental discovery of calcite spherulites forming on colonies of various halophilic bacteria grown on solid Luria-Bertani medium made containing water from a brine pool in Death Valley, their natural habitat. Further studies with a large spherulite forming bacteria, Pseudoalteromonas haloplanktis, showed that calcite precipitation conditions were the consequence of bacteria using amino acids as a source of carbon and energy, a metabolism that produces NH3 and CO2 waste products. NH3 raises the pH of the medium, turning CO2 into CO32-. Calcium in the natural brine combines with CO32-. The resulting spherulitic calcite precipitation is nano-acicular due to organo-mineral interactions with amino acids. As the bacterial colony grows larger in size, new rows of calcite spherulites emerge outside the old row and a few millimeters inside the colony’s active edge. Starvation kills bacteria in the colony center. Living bacteria degrade dead bacteria recycling them for energy, a process that expels PO43- as well as NH3 and CO2 into the medium. PO43- eventually reaches inhibitory levels that stop further calcite spherulite growth. Calcite spherulite growth eventually resumes once inhibitory PO43- was removed by struvite precipitation. Calcite growth resumed then switched to micro-prismatic until the precipitation of orange guanine monohydrate at the colony center, at this time, 3-fold calcite coats spherulites. This study sheds light on the formation and inhibition of calcite spherulites found with infection induced urolithiasis, a medical condition referring to stone obstructions in the human urinary tract. Similar formations are also found in mollusks and stromatolites. All these examples are morphologically similar due to the inevitable presence of amino acids, peptides, or proteins with various degrees of biological control. A case is made that understanding simpler bacterial biomineralization processes can also illuminate formation processes of the more complex.
biomineral; Guanine monohydrate; halophile; pseudoalteromonas; Spherulite
Microbiology | Mineral Physics
University of Nevada, Las Vegas
Jibrin, Zakaria, "Calcite Spherulite Formations and Their Controls in Halophilic Bacterial Cultures" (2022). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4593.
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