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

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.

Insights into the amorphous calcium carbonate (ACC) → ikaite → calcite transformations

“…These maxima are commonly reported for synthetic ACC 7,56,57 and those at 0.280 and 0.200 nm were also reported for slime-mold ACC. 5 The The thermal decomposition and behaviour of ACC (I) were investigated using TG-DSC (Fig. 1e-g and S1a-c †).…”

“…Crystalline anhydrous and hydrous calcium carbonates are widespread on the Earth's surface 1 and commonly associated with life. [2][3][4][5] The first calcium carbonate to precipitate is often amorphous and metastable and referred to as amorphous calcium carbonate (ACC). [6][7][8] It plays a key role in biological mineralization and in the Ca uptake of living organisms.…”

“…[6][7][8] It plays a key role in biological mineralization and in the Ca uptake of living organisms. 3,5,9,10 ACC occurs widely in nature, such as in the skeletal materials of Clathrina lime sponges, scleractinian corals, Pyura pachydermatina tunicates, Strongylocentrotus purpuratus sea urchin embryo, and Biomphalaria glabrata snail embryo, [11][12][13][14] and has also been reported from cave bacteria 3,15 and slime molds. 5 Revealing the conditions under which ACC crystallizes can provide insights into the type of calcium carbonate that is formed.…”

“…3,5,9,10 ACC occurs widely in nature, such as in the skeletal materials of Clathrina lime sponges, scleractinian corals, Pyura pachydermatina tunicates, Strongylocentrotus purpuratus sea urchin embryo, and Biomphalaria glabrata snail embryo, [11][12][13][14] and has also been reported from cave bacteria 3,15 and slime molds. 5 Revealing the conditions under which ACC crystallizes can provide insights into the type of calcium carbonate that is formed. 16,17 Its transformation is affected by a range of factors including pH, temperature, pressure, presence of additives, water content, and mechanical effects.…”

“…In particular, Zou et al reported that the ACC precursor to ikaite contains ∼6 mol water, 30 which is significantly higher than typically measured in ACC. 4,5,7,46,47 Furthermore, it is unclear how the precursor and ikaite-formed ACCs influence the formation and transformation of ikaite, i.e., the geochemical data during transition. 48 The characterization of ACCs and their targeted preparations can aid in the synthesis of additive-free material for industrial applications.…”