An exceptionally stable and widespread hydrated amorphous calcium carbonate precipitated by the dog vomit slime mold Fuligo septica (Myxogastria)

Laurence A J Garvie,Péter Németh,László Trif

doi:10.1038/s41598-022-07648-9

Abstract

Biogenic amorphous calcium carbonate (ACC) is typically metastable and can rapidly transform through aging, dehydration, and/or heating to crystalline calcium carbonate. Gaining insight into its structure and properties is typically hampered by its tendency to crystallize over short time periods once isolated from the host organism, and also by the small quantities that are usually available for study. Here we describe an exceptionally stable hydrated ACC (HACC) precipitated by the cosmopolitan slime mold Fuligo septica (L.) F.H. Wigg. (1780). A single slime mold can precipitate up to a gram of HACC over the course of one night. Powder x-ray diffraction (XRD) patterns, transmission electron microscopy images, infrared absorption spectra, together with the lack of optical birefringence are consistent with an amorphous material. XRD simulations, supported by thermogravimetric and evolved gas analysis data, are consistent with an intimate association of organic matter with ~ 1-nm-sized ACC units that have monohydrocalcite- and calcite-like nano-structural properties. It is postulated that this association imparts the extreme stability of the slime mold HACC by inhibiting loss of H2O and subsequent crystallization. The composition, structure, and thermal behavior of the HACC precipitated by F. septica collected over 8000 km apart and in markedly different environments, suggests a common structure, as well as similar biochemical and biomineralization mechanisms.

Highlights

Biogenic amorphous calcium carbonate (ACC) is typically metastable and can rapidly transform through aging, dehydration, and/or heating to crystalline calcium carbonate
Characterization of biogenic ACC can be challenging for several reasons given that only small quantities are usually available, its presence may be masked by crystalline calcium carbonates, and because of its tendency to crystallize over short time periods once isolated from the host organism
The powder x-ray diffraction (XRD), electron diffraction, and infrared spectroscopy (IR) data, together with the lack of optical birefringence are consistent with the F. septica hydrated ACC (HACC) spheres as an amorphous material with sub-nanometer-sized diffracting domains

Summary

Introduction

Biogenic amorphous calcium carbonate (ACC) is typically metastable and can rapidly transform through aging, dehydration, and/or heating to crystalline calcium carbonate. Our data are consistent with an intimate association of organic matter with ~ 1-nm-sized ACC units that have monohydrocalcite- and calcite-like nano-structural properties. 19% of the mass is lost in the case of samples measured in air, and 15.1% when heated under He. This ~ 4% difference sets a minimum in the FSY sample on the organic content as some is pyrolytically degraded under He. The quantity of organic matter can be estimated from the compositional data

Results

Conclusion